Greening Cities

Beautiful suburban gardens are disappearing as old houses are pulled down to make way for new large ones, dual occupancies or apartment blocks built with very little garden and few trees. Maybe we sigh and wonder what the world is coming to, but there are some moves in the opposite direction. Vision 202020, started in 2013, is an attempt to increase green space in Australia’s cities by 20% by 2020 to future-proof them so they can cope with a warming climate and pressures of modern living.

So far, there are 364 organisations in its network. See  Many government bodies, including local government, have signed up to it, are aligning their planning with it and are establishing specific projects to achieve this vision. Nationwide signatories include cities of Adelaide, Campbelltown, Ballarat, Central Goldfields, Canterbury, Melville, Fremantle, Gold Coast, Geelong, Stirling, Subiaco, Sydney, Vincent, Launceston, North Sydney, Penrith, Mundaring, Banyule, Darebin, Kingston, Melbourne, Yarra, Moreland and Whitehorse. Many other organisations, including 23 developer, construction companies have signed up along with many landscapers.

Why green cities?

There are many reasons to increase green space. See our previous article by Dr. Gregory Moore for more detail.  Trees and other greenery moderate temperature and associated human comfort through shading, protecting from wind and through evapotranspiration. They also reduce glare and noise.1 These functions of vegetation lead to human health benefits such as reducing the cancer risk of sun exposure, reducing heat-related illness, improving mental wellbeing and reconnecting children with nature to improve their creativity and physical activity.

These benefits, in turn, flow on to economic benefits such as increased property values due to the aesthetics of trees and gardens, reducing costs of infrastructure and mechanical heating and cooling through shading and reducing health costs.  A well-vegetated suburb has decreased costs of maintaining storm water systems because vegetation slows water flow and reduces soil erosion.

At least equally important are benefits to nature and ecosystems by absorbing carbon dioxide and providing wildlife habitat.

The big challenge

largehouse1Urban green space has been decreasing since the 1980s. Then, houses typically took up 20 – 30% of house lots but by 2010 they took up at least 35-40%. So backyards shrunk from 150 square metres to an average of 100 square metres.  This reduction in green space was not due to urban consolidation, but to growth of house sizes – in the 1980s it was an average of 161 square metres, but by 2012-13 it was 241 square metres – a 50% increase! This means that green space in suburbs is increasingly in the form of very narrow strips between and behind houses – spaces that are not particularly useful for growing canopy trees, providing wildlife corridors or for outdoor relaxation or children’s play.

Progress so far

Most of the projects associated with Vision 202020 have involved research, data gathering, policy and planning. These include:

  • A database which shows which plants grow best under what conditions
  • Developing a simple soil testing kit
  • Developing a straightforward process to bring together councils, residents and businesses to create a collaborative low cost composting program
  • Projects associated with funding and investment such as how best to share risks and costs of creating more green space
  • A directory of good design which showcases examples of creating or improving green space
  • An approach to creating common green space when individual dwellings have little or none around them
  • Expanding Permablitz so that more people and organisations can access methods of permaculture
  • A process for creating a community action plan to involve more people

Is this just all talk and paper work?

It might look that way, but meeting the somewhat ambitious goal of 20% more green space in just 7 years requires development of innovative and clear approaches to getting the work done.

One of the most interesting projects is a workbook How to grow an urban forest.  This was the result of collaboration of different levels of government.  Aimed primarily at local councils, the workbook sets out 10 very clear steps.  A key component is engaging the broader community, explaining why it is so important that there is more green space and enlisting their aid rather than just changing planning laws and planting trees on council-owned property. This book contains examples of cities that have started the process of greening.

What can gardeners do?

As gardeners seeking a more sustainable world, we are probably saddened as we see gardens engulfed by multiple occupancies and houses of monumental size. Do we really need such large houses? Can we convince State and Local governments to change planning laws that permit this gobbling up of green space by over-sized buildings?

As individuals, there are many things we can do:


  • Create green walls and roofs.  Research is advancing on the best plants, soil and growing conditions. An excellent example of such research is being conducted at the University of Melbourne, Burnley Campus (shown at right).  Many businesses are providing systems to enable these for homeowners.
  • Grow canopy trees
  • Plant tall shrubs and creepers along fence lines and walls
  • Replace hard surfaces with vegetation – grass and lawn alternatives work well for walkways and driveways. There are now systems for providing a rigid underlay for grassed driveways.
  • Encourage family, friends and organisations to which you belong to green-up
  • And, if you are politically-minded, you can approach your local council and support their initiatives to green your local area.
  1.   Hall T. 2010. The life and death of the Australian backyard. CSIRO Publishing.

What Gardeners Can Do About Climate Change

Worried about climate change?  Gardeners are in a great position to do something about it - even if it is not a lot, every bit counts!

We know that scientists have been warning about the warming climate for the last 30 or more years, but it has taken a long time for governments to recognize that it exists.  Those of us who are close to our gardens and the land have seen the effects already happening.

At last the United States government Environment Protection Authority has issued a report1 telling communities to be prepared for the effects of the increasing natural disasters as a result of a warming world. But we need to be taking action NOW to try to slow the rate of global warming that is causing these events.

Vegetation Cover

We all know that Landcare groups have been planting trees for many years to prevent erosion on degraded land. Fortunately, these plantings also help take up carbon dioxide from the atmosphere – as long as they become permanent carbon sinks. However, the rate and amount of greenhouse gas removal by trees is not as high as the emissions from use of fossil fuels, so very large areas of land need to be devoted to forests2.

Gardeners can help by planting as much vegetation as possible - even lawn helps!   And by avoiding concrete in paving and walls since it creates high greenhouse gas emissions in its manufacture.

And don't forget green walls and roofs!  Not only do they add more plant cover, but they add insulation to buildings, so reducing energy use in heating and cooling.

But although these actions are important, there is much more gardeners can do!.

Our Diet

Many people are now realizing that we can reduce the rate of global warming by consuming less meat and dairy products3. Eliminating meat from the diet reduces greenhouse gas emissions by approximately 50% because there are fewer methane-producing animals required to produce food 4. In contrast, fruit and vegetable production draws down carbon dioxide through photosynthesis.  So even just reducing the number of times you eat meat per week will make a difference. On top of this, to provide the same amount of nutritious food, meat production uses up more land as pasture than growing fruit and vegetables.  So when gardeners grow fruit and vegetables at home or in a community garden they are making a contribution to slowing climate change,

If you are doing that already, you also know about the added health benefits. More plant-rich diets address many growing health problems including heart and circulatory problems 5, some forms of cancer 6 and even rheumatoid arthritis 7 by reducing dependence on meat.

Reduce Shopping Miles by Buying Local Goods

Even if we have extensive gardens and eat plant-rich diets, there is a lot more we can do regarding our levels of consumption.

Food Miles

We are hardly ever totally self-sufficient for food and still purchase items which may have travelled many miles to reach us, using fossil fuels in the process. So let’s try reducing food miles by buying food from local growers when we cannot produce it ourselves – think Farmer’s Markets, Harvest Swaps and foraging for food.

Other Goods

We can seek out other items for the garden e.g. furniture, stakes or pots, which are produced in Australia – or even better in our own state – rather than those that are imported. This may mean a higher financial cost, but that may encourage us to . . . .

Reduce, Reuse, Recycle

We can become thrifty gardeners!

Being clever about minimizing our purchases, reusing items and recycling what we can’t reuse in their current form means less waste, less resource use (including less coal-fired electricity) and less waste going to landfill which would lead to methane production.

For example, we can minimize use of plastic pots for seedlings by making containers using the centres of toilet rolls as the sides and some newspaper in the bottom. In fact, newspaper can be used to make complete seedling pots.  Both alternative types of “pot” are also better for seedlings since the whole “pot” plus seedling can be popped directly into a garden bed without disturbing the roots – the cardboard or paper will gradually decay.

Some clever ideas for reusing and recycling in the garden have been used in the garden of one of SGA's subscribers.  Recycled materials can be used for garden edging and garden art.


Sending organic waste to landfill results in methane because decomposition occurs in the absence of oxygen.  In contrast, composting it, either at home or commercially, reduces methane production and, although aerobic composting as In your compost heap produces some carbon dioxide, application of the finished product to soil helps soil to retain carbon as well as increasing its fertility.

Fertilisers and Pest Control

Try to use as many natural methods to enhance soil quality and fertility.  Compost or worm castings/ tea from your own green/food waste have involved no fossil fuel use and relatively low carbon emissions. If you are growing vegetables, crop rotation employing a green manure cycle reduces the need for external inputs of any sort.

Manures from your chooks or collected from farms are almost as good, involving only the carbon inputs from their food and transportation.  Other products such as blood and bone, fish meal, seaweed extract, compost and natural minerals e.g. organically certified phosphorus are less energy-intensive than chemical fertilisers that have gone through complex extraction and manufacturing processes.

Using integrated pest management techniques and companion planting will minimise the need for energy-intensive manufactured pesticides needed to control insects, weeds and disease.



2. Baldocchi D, Penuelas J. (2018). The physics and ecology of mining carbon dioxide from the atmosphere by ecosystems. Climate Change Biology 

3. Hedenus F, Wirsenius S, Johansson DJA (2014) The importance of reduced meat and dairy consumption for meeting stringent climate change targets. Climatic Change. 124 (1–2): 79–91.

4. Hoolohan C Berners-Lee CM, McKinstry-West J, Hewitt CN. (2013) Mitigating the greenhouse gas emissions embodied in food through realistic consumer choices. Energy Policy 63: 1065-1074.

5. McEvoy CT, Temple N, Woodside JV (2012) Vegetarian diets, low-meat diets and health: a review. Public Health Nutrition 15 (12): 2287-2294.

6. Prashanth Rawla, Tagore Sunkara, Adam Barsouk (2019) Epidemiology of colorectal cancer: incidence, mortality, survival, and risk factors.

7. Philippou E and Nikiphorou E. (2018) Are we really what we eat? Nutrition and its role in the onset of rheumatoid arthritis. Autoimmunity Reviews 17(11): 1074-1077.

Gardening Trends 2018-2019

Like many activities we engage in, gardening is subject to fashion and trends.  So what are the current directions?  Do they have anything to do with changing gardening’s impact on the planet?  Or with healthy food production?

We consulted online articles from 12 different organisations which provided their analysis of garden trends for 2018 – 2019. We can identify 17 different trends, among them 9 were noted by 2 or more organisations.  Although we present them as though they are part of a competition and allot them places, being a "winning" trend does not mean we endorse it or encourage you to follow.

The “Winning” Trends


1. Outdoor Rooms

Identified by six organizations, bringing features of the indoors to the outside is top of the list. Features to be included outdoors were comfortable soft seating, cooking facilities, fire-pits and sometimes even an area which is just like a room with roof and rain-and wind-proofing via zip-up plastic blinds.

2. Sharing 2nd Place

Five organizations noted these trends:

a. Edible Gardens

This type of garden is either in the form of dedicated vegetable patches (like that at the top of the page) or “foodscaping” i.e. including edibles among other plants for both their edible and decorative values.

b. Robo-Gardening

A new term that indicates the use of technologies ranging from apps, drones, automatic watering systems and moisture detectors to motorized awnings, LED lighting and glow rocks.

3. Sharing 3rd Place

These trends were identified by four organisations.

a. Indoor Gardening

This takes the form of any style of indoor plant growing - ornamental plants in individual pots, jarrariums, edibles or herbs and even whole plant walls in restaurants. Apparently the share of revenue from indoor plant sales in growing nurseries has increased by 1.7% worldwide (The Age, 24-03-2019).

b. Climate Change Gardens

Included in this trend are gardens that minimize water use by using drought-tolerant and resilient plants, that recycle both hard and soft materials, reduce chemical use and are extra low-maintenance.


4. Shared in 4th Place

These were noted by 3 organisations:

a. Habitat Gardens

These use native plants specifically to provide food and shelter for native birds and animals.

b. Home Sanctuary Gardens

Those that provide features to enhance contemplation and a peaceful atmosphere. They include water features and Zen gardens with raked stones and a few carefully placed plants or ornaments.

5. Sharing 5th Place

Two trends were identified by 2 organisations.

a. Texture

This is the use of a greater variety of textures in wall and ground treatments – pebbles, brick and sand combinations, wood and natural stone in combination, growing grass or other ground covers in between pavers and decorative mulches around plants.

b. More Attention to Plants than Hard Structures

There seems to be a tendency to give gardens their structure and contrast through different size and types of plant rather than using walls and hard features.

6. Eight other trends were identified:

Just one organisation listed these:

  • Younger people (millennials) engaging in gardening
  • Window Gardens – designed to be viewed through a window
  • Topiary
  • Unusual Features - painted rocks or sculptures and other ornaments
  • Bright colours - either as flowers or furniture
  • Concrete everywhere – from pavers, flooring, barbecues to even kitchen benches in outdoor rooms
  • Swimming pools
  • More professional design

What can we conclude?

Are we seeing a tendency to integrate more with the natural world?  Many trends suggest that - outdoor rooms, indoor plants, more attention to plants in landscaping, greater focus on growing our own food, providing habitat and reducing impacts through climate change gardens.

But is having outdoor rooms that are just like indoors indicative of sustainability when they duplicate indoor facilities, waste resources and shut nature out?  What about robo-gardening, concrete everywhere, bright unnatural colours and contrived artificial topiary – are they attempts to dominate nature for our own ends?  Robo-gardening may, in the long run, reduce water use and make monitoring more efficient, but the use of electricity for motor-driven machines and other devices, tends to replace human energy and brain power with largely coal-fired power.

Maybe these contrasting trends are in different parts of our society – those who recognize they are part of the natural world and wish to be closer to it, protect it and reduce climate change and its impacts and those who wish to control it or who see it as threatening or too difficult to manage while they fulfill their personal needs.

At SGA we are delighted to see the trends towards eco-friendly gardening, waste minimization, water saving, wildlife protection and local food growing, especially among millennials who are now 29% of gardening households!  We try to encourage these trends, provide the tools to do so and we depend upon you to do the same.

Are Plants Intelligent?

In the 1980’s, mentioning that plants could communicate or that they might be intelligent used to draw the response “Are you crazy?” when this was then proposed by scientists.  Perhaps this reply derived from “hippy” suggestions that we should talk to our plants to make them grow better.  But now there is solid evidence the plants can, indeed, respond to information in the rest of the world, respond to those messages in a variety of ways including sending messages to each other. The idea is emerging that the plant kingdom is a complex society in which members share information and subsequently respond, in a way similar to we do in human society, but using different languages1. Some scientists, therefore, suggest that plants possess intelligence2.

Plants show a number of behaviours that appear to be more than just a simple stimulus and response, but which involve communication both within and between plants.  They respond to temperature, gravity, light, moisture, infections, concentrations of oxygen and carbon dioxide, predation, physical damage and touch.  Let’s look at some of these in more detail.

Defending from attack

Early studies of willows, poplars and sugar maples showed that trees near those that were being attacked by insects started to release a range of chemicals which acted as repellents to those insects – somehow they “knew” that they were threatened by attack themselves. Others plants whose shoots were infected by disease, could release gases into the air which signalled the threat to plants close by so stimulating them to strengthen their own chemical defences.  The gaseous chemicals released were different for different types of injury.

Snail1Some plants have more complex “behaviours”.  For example, some whose roots were being attacked released gaseous substances which attracted nematodes which then killed the predator3. Others could interact with ants which protect them against attack by organisms which eat them, against disease and against competing plants4.

After hornworm attack, one species of the tobacco plant accumulated nicotine which blocked particular nerve receptors in other predators reducing their ability to attack the plant.  Some of the chemicals used in transferring information between plant cells are the same as those found in humans.

When sagebrush plants were clipped they produced a gaseous chemical (methyl jasmonate) that stimulated neighbouring wild tobacco plants to increase their defensive biochemistry.  These tobacco plants were then more resistant to subsequent attack by grasshoppers and cutworms5.

plantcutSo would this mean that having a hedge, which we clipped regularly, near our veggie patch would reduce insect attack?  An intriguing but, as yet, unproven possibility.

Ensuring reproduction

Plants have developed strategies to increase their reproductive chances. It was, in fact, Charles Darwin in the 1860s, who wrote that plants had “responded” to the characteristics of birds and insects so that their sexual organs were appropriately shaped to allow access for pollination3.  These pollinators were then “rewarded” with nectar which was attractive to those pollinators and essential to their diets.

Some species of the Arum family produce a dung-like odour – exactly the same chemicals that are exuded from dung where the insects necessary for pollination of the Arum plants gather.


Most of us are aware that members of the Fabaceae (legumes such as peas and beans) “domesticate” the Rhizobium bacteria in nodules on their roots in return for supply of nitrogen which the bacteria can fix from the atmosphere.  It seems too, that the Rhizobium bacteria produce hormones, cytokinins and auxins, which affect how the plant root behaves in growing to seek nutrients6.

Mycorrhiza as information networks

Perhaps even more interesting is how plants communicate through mycorrhizal networks.  These are filaments of fungus that either penetrate the cells of plant roots, or sit on their surface.  It is thought that 80 – 90% of plants have mycorrhizal associations7 and there are many tens of metres of filaments per gram of soil.  These filamentous networks are better at absorbing water and nutrients than the plants themselves and thus they transport and exchange these compounds, increasing their absorption by plants up to 1000 fold.

They also facilitate sending “messages” between plants. Experiments have shown that bean plants infested with aphids can send signals to other plants when above-ground communication was blocked by physical barriers.  The plants receiving the messages then produced chemicals which attracted other insects which were predators of the aphids8.

Nerve-like signaling within plants

It is well established that electrical as well as chemical signals are transmitted through plants in response to various stimuli such as damage. These signals seem to be via waves of reactive oxygen molecules and calcium ions.  Although signaling in the nerve systems of the animal kingdom is mediated through potassium and sodium ion movement, the overall mechanism is similar9.

Very recent work from Australia researchers has shown that when plants are touched by humans, tools or even insects, their equivalent of an immune system is turned on and, because that uses plant resources, it can cause reduction in growth10.  However, earlier research has shown that rubbing the leaves of can stimulate some plants defend themselves from fungal attack - also via this immune system-like pathway.11


Researchers are not claiming that plants have brains or can think rationally, but that they communicate in many ways that have similarities to human communication and intelligence.  We should understand this if we are to both care for plants and benefit from them.

These studies provide a scientific basis for companion planting where certain plants have been observed to protect others from predation or disease.  It’s not clear yet whether we might intentionally damage some plants, or plant sacrificial crops, in order that they alert others to strengthen their defences. But we should probably be gentle with the soil everywhere in gardens and forests so that the benefits of communication through mycorrhizal networks are not destroyed.

  1. McGowan K.  2013.  How plants secretly talk to each other.  Wired 12: 13.
  2. Trewavas  A. 2005.  Green Plants as Intelligent Organisms.  Trends in Plant Science 10: 413-419.
  3. Baluška F, Mancuso S, Volkmann D (Eds.)  2006.  Communication in Plants. Neuronal Aspects of Plant Life. Springer Verlag.
  4. Brouat C, Garcia N, Andarry C, McKey D.  2001. Plant lock and ant key: pairwise coevolution of an exclusion filter in an ant-plant mutualism. Proc R Soc Lond Ser B 268: 2131–2141.
  5. Karban R et al. 2000. Communication between plants: induced resistance in wild tobacco plants following clipping of neighboring sagebrush. Oecologia 125: 66-71.
  6. Castro O, Bucio J L.  2013.  Small Molecules Involved in Transkingdom Communication between Plants and Rhizobacteria, in Molecular Microbial Ecology of the Rhizosphere: Volume 1 & 2 (ed F. J. de Bruijn), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9781118297674.ch28
  7. Australian National Herbarium. 2013.
  8. Babikova Z et al. 2013.  Underground signals carried through common mycelial networks warn neighbouring plants of aphid attack. Ecology Letters 16: 835–843.
  9. Choi W et al.  2016. Rapid, Long-Distance Electrical and Calcium Signaling in Plants. Annual Review of Plant Biology 67: 287-307.
  10. Yue Xu et al.  2018. Mitochondrial function modulates touch signalling in Arabidopsis thaliana.
  11. Benikhle L., et al. 2013. Perception of soft mechanical stress in Arabidopsis leaves activates disease resistance. BMC Plant Biology13:133.

Carbon Emissions from Gardening

In a previous article we explored ways that gardeners can lock up carbon in the soil.  Although increasing soil carbon is important, it doesn’t address ways of dealing with greenhouse gases that are talked about less often, namely, methane and nitrous oxide.  Fortunately, the approaches to reducing emissions of these gases also lead to better soil structure and fertility.


This gas, with the chemical formula CH4, (i.e. each molecule contains one carbon atom) is worrisome because it is 25 times more potent than carbon dioxide in its global warming impact, weight for weight. However, it decays more rapidly in the atmosphere than carbon dioxide. It is produced naturally from wetlands and as a result of the digestive processes of ruminant animals (cows and sheep). It also leaks from natural gas systems.1

The major pathway for methane to be generated by gardening activities is through breakdown of organic matter in anaerobic conditions i.e. when oxygen is excluded. Gardeners may cause extra methane to be added to the atmosphere by some methods of composting and making weed “tea”, soil compaction and poor pond maintenance.


We all want compost, don’t we? But significant amounts of methane can be produced in the centre of compost heaps as material is broken down and the temperature rises. Methane production appears to be due to the density of the heap so that oxygen cannot penetrate and anaerobic microorganisms are favoured. To reduce this problem the heap needs to be well aerated. You can do this by:

  • compost500Making your own compost bin or bay out of material that lets air through i.e. not solid plastic. Suitable materials are timber slats, logs or trellis or chicken wire.
  • Building the heap with a wooden pallet as the base. This gives some air space under the heap.
  • Adding material such as straw that doesn’t get compacted so easily.2 Make sure that there are plenty of dried leaves, twigs and other fibrous materials in the heap. These are best added in layers with the amount of dry material about equal to the amount of wet/green.
  • Including vertical aerating tubes as you build the heap. These can be made from tightly rolled chicken wire or PVC pipe with lots of holes drilled into it. Such devices have the added advantage of making it easy to get water into the centre a heap which is drying out.
  • Using a tumbling device.
  • There are a number of different designs for tumblers commercially available. If these are rotated every day or tumbler1so, they will aerate material satisfactorily. However, they sometimes lead to lumps which can get aerobic, if enough dry material is not added at the same or, indeed, mixed with the wet material before adding it. Actually turning the tumbler can be a problem since it can get quite heavy.
  • For a thorough coverage of managing a tumbler see
  • If all else fails, you can engage in some physical exercise and turn the heap regularly. You can do this with a garden fork (easier than a shovel), but it can be backbreaking work. There are various compost turning tools available now, such as one which looks a bit like a large corkscrew. It twists down easily and then you can pull out a plug of material from further down the heap.

Making weed “tea” under anaerobic conditions

Here is a dilemma. In a previous article we explored how to make compost, worm and weed teas to produce soluble fertilizer and discussed how the solid material needs almost constant stirring to avoid anaerobic conditions. We also pointed out that it may be easier for home gardeners to use the anaerobic method with only occasional stirring. Given that this method favours methane production, you might have a bit of a debate with yourself about the relative costs and benefits of each method or choose other ways of processing garden waste such as solarizing or composting.

Compacting soil

This happens by placing heavy weights on it e.g. heavy machinery or walking. Compaction removes the air spaces which aerobic microorganisms need for their oxygen supply. It is less likely to happen in raised garden beds and if the bed width is limited to about 1 metre so that you can reach across.

pond500Pond Maintenance

Ponds can become anaerobic if the water gets very murky or if the surface gets too much growth of water weeds such as Azolla3 as in the image on the right.  These conditions can limit light entry so that submerged oxygenating plants are killed. Adding unsuitable fish species which stir up sediment can have a similar effect.


Nitrous oxide

Although it does not contain carbon atoms, nitrous oxide, N2O, is 298 times more potent as a greenhouse gas than carbon dioxide, but is shorter lived, persisting in the atmosphere for 114 years. So we should not just think about carbon emissioins from gardening!

It has been calculated that 40% of emissions of this gas in the USA come from human activities with about 70% of that derived from agricultural land management. Nitrous oxide also happens to be the most important gas contributing to the hole in the ozone layer now that halocarbon levels are declining.

To reduce extra nitrous oxide being emitted we can:

  • Use manures and other organic sources of nitrogen rather than synthetic nitrogen fertilisers and apply them carefully so that there is not excess nitrogen for plant use – that means not applying them when plants are not actively growing.  Synthetic nitrogen fertilisers also contribute to making soil more acid.
  • Since acid conditions encourage biochemical pathways that produce nitrous oxide, if soil pH is low we can add lime or dolomite.
  • Use no-dig methods to avoid soil disturbance.
  • Turn garden waste into compost or mulch rather than burning it.
  • Avoid working soil when it is wet as this assists compaction which creates conditions in which soil micoorganisms convert nitrates to nitrous oxide.
  1. Reay D, Smith P, van Amstel A. 2010. Methane and Climate Change. London: Earthscan. ISBN978-1844078233.
  2. Sommer SG, H. B. Moeller. 2000. Emission of greenhouse gases during composting of deep litter from pig production – effect of straw content. 2000.  J. Agricultural science 134 (3) 327-335.
  3. Rachel A, Janes JW, Eaton K . 1996. The effects of floating mats of Azolla filiculoides and Lemna minuta Kunth on the growth of submerged macrophytes. Hydrobiologia 340 (1) 23-26.

Compost, Worm and Weed Teas

If you are a gardener who tries to reduce your impacts on the natural environment, you will be using methods which avoid manufactured fertilisers, pesticides and herbicides and which minimize waste. So you’re into composting and worm farming and mixing the resulting solid material into the soil. However, at many times of the year a liquid fertilizer in the form of a “tea” may give plants, especially vegetables and fruit trees, a boost that is quicker than applying the manure, worm castings or compost which release their nutrients much more slowly. Such teas can be made from compost, weeds and other greenery and manures. How do you make and use them? What are their pros and cons?

The advantages of using teas are said to be:

  • They provide nutrients for you plants more quickly in the soil than the solid material used to make them.
  • The microbes in them make soil nutrients available and help prevent soil and plant diseases, something that commercial fertilisers do not do.
  • They are cheaper than commercially manufactured fertilisers.
  • Unwanted plant material in your garden can be turned into something really useful.
  • They make the garden more self-sufficient by recycling material it has produced.

On the other hand, because the effect of teas depends on the quality of the starting materials, how the teas are made, the climate, when they are applied, the plants they are used on and the state of the soil before their use, there is debate about their usefulness, with some findings that they can be harmful.

Extracts and teas

Don’t confuse extracts and teas. The simplest, but not the best, method of making a liquid fertiliser from your garden material is to make an extract. This is made by covering some compost, worm castings or manure with water for a few hours or days. Nutrients and minerals from the solid materials dissolve in the water and microorganisms present on the solids can enter the liquid. This can then be used by either applying directly to the soil or, when diluted to the colour of weak tea, as a foliar spray. However, these extracts are inferior to teas which have been brewed.

Why bother making a tea?

If properly brewed, teas provide much more than minerals and other nutrients. They are also very rich in microorganisms, a mixture of bacteria, fungi, protozoa and nematodes, which can fight plant disease-causing organisms in the soil and on foliage and can convert soil nutrients into forms that can be taken up by plants. They usually take longer to make than extracts and may involve more effort. For many gardeners and organic farmers, making compost tea is both a science and an art. And there are many different opinions about what method is best and, indeed, whether they work at all.

Compost tea

To prepare compost tea, put mature compost into a container like a bucket or plastic rubbish bin. You can put compost straight into it or into a “bag” which can be made from a piece of shade cloth or other material with small holes like old net curtains, stockings of panty hose. Cover the compost with water. It is preferable to use rain water, filtered water or mains water that has been allowed to stand for 24 hours to allow the chlorine to off-gas before adding to the weeds. The removal of chlorine makes it easier for microorganisms to multiply. You will need to add something to start the process off by providing easy to access nutrients for microbial growth. The best additions are brown sugar or molasses but others could be some fish meal, some canned fish which has been allowed to “go off”, grain meal, fish food, rotten fruit, compost, garden soil or finished compost. Nitrogen rich vs sugar rich additions give different results in terms of favouring bacteria or fungi.

Then there are two ways you can brew the tea:


This requires aeration. This process provides oxygen which allows aerobic microorganisms to multiply rapidly and break down the plant material. You could use a stick, which means you will need to stir it several times a day for about 10 days. In between stirring, cover the bucket or bin loosely so that air can enter. But unless you really like physical exercise and can remember to stir each day, using a fish tank aerator for about 3 days is a good alternative. There are many websites which provide ideas for you to make your own compost tea aerator, and there are even some commercially available assemblies.

Tea made this way will not smell unpleasant and should be used straight away. There are different opinions about how long the tea should be brewed. It really depends on your compost, the temperature and the nature of aeration. At some point, aerobic microorganisms will have used available nutrients and not be getting enough oxygen, so anaerobic microorganisms will take over. At this stage it will start to smell wiffy – but don’t despair. You can use it quickly before the aerobic microbes all die (because there will always be a few aerobic microorganisms) or let it go on brewing under anaerobic conditions.


Some practitioners recommend that it might be better for home gardeners to use the easier anaerobic method which does not involve aerating and favours microorganisms which do not require oxygen. Just cover the container fairly firmly and wait for about 3 weeks. It requires longer and tends to be smellier but still produces a useful product. Some say that after the anaerobic microbes have finished, aerobic ones will take over again. But as I indicated, there is some controversy over this.

Worm tea and worm farm leachate

Most of us are also familiar with the liquid that comes out of the worm farms – called names such as worm wee, worm juice or worm tea, but really is a leachate. It contains plant nutrients, but is not rich in microorganisms like compost tea. Worm leachate really needs to be used cautiously since it contains “bad” bacteria as well as “good” and may be harmful to plants, especially if it smells “off”.

For worm tea, the castings from a worm farm can replace compost in the teas described above.

IMG_0005Weed tea

The best weed tea is made from plants with deep roots like comfrey, dandelion and nettle since they have incorporated minerals that have been leached from topsoil. Making weed tea is also a great way of extracting nutrients from plant material you don’t want in either your garden or in your compost heap where they would start multiplying. It also includes plants with runners and those which take root easily.
Follow the methods described for compost tea but it may be necessary to weigh the weeds down between stirring because they may float.

Manure tea

Animal manure can be used to make a tea by the same methods as for compost tea. However, there is a high risk of producing a brew which contains organisms which can be harmful to both plants and humans, especially if it is anaerobic. An extract, however, is a quick way making a nutrient-rich solution, but it will not have the same benefits as a microorganism-rich aerobic tea.

Using teas

Remove the bag which contains the solids and let it drain into the container. Or if you haven’t used a bag, pour the liquid through some shade cloth or other fine material laid in a soil sieve. It would be wise to do this wearing rubber gloves (and perhaps a peg on your nose!) since this might be a pretty potent and smelly brew. Put the solid material into your compost heap where it will break down further.

Remember, teas contain living organisms and should be treated with respect. Sun and heat can kill them, so apply them to the garden early in the morning or after dusk. The most useful times of the year to use them appear to be early spring, several times during the growing season and towards the end of autumn so that the organisms can work in the soil over winter.

Handle the brews carefully with gloves and don’t apply to vegetable leaves that will be eaten, especially if anaerobic and smell bad, since it is possible that pathogenic organisms are present. Use the tea diluted one to ten as a foliar spray, or less diluted if applying to soil.

And don't expect miracles - results depend on so many factors that they are impossible to predict. We'd be interested in hearing of your experience.


Lowenfels J and Lewis W. (2010) Teaming with microbes. Timber Press, Portland, Oregon.
What are the Benefits of Aerated Compost Teas vs. Classic Teas?
Secrets of Making Compost

Gift Ideas for Sustainable Gardeners

If you're like me, come the beginning of December, I'm scratching my head to think of suitable presents that might be appreciated by the recipients.  Even if I'm giving to someone who isn't really a gardener or not particularly interested in sustainability, it feels better to give something that I know is not just going to add further pollution to the world, but something that might improve it a bit.  So here are some ideas - some are more suitable as gifts for avid sustainability devotees, but others could be given to anyone.

Gardening Gifts

Recycled planter

Although an obvious gift for a gardener is a plant of some sort, why not make it more special by supplying it in a container that is made from something recycled and is also decorative.  It could be something simple and home made, as in the image on the right or it could be something more decorative and perhaps bought from a store.


Avid gardeners are always pleased to receive seeds, especially if they are heirloom varieties.  This type of seed, obtainable from specialist seed suppliers, enables preservation of old genetic types that are being lost as large seed companies breed types that are quick to grow in order to please a mass market.  Many of the newer seeds arise from cross-breeding of 2 different varieties to yield plants with particular characteristics e.g. colour or vigour.  If seed from that type of plant is saved and subsequently sown, there may be no offspring at all, or, if there are, the offspring will not be like the parent plant. In contrast, plants grown from heirloom seeds will produce fertile seeds which can be saved and used to grow the same plant in subsequent years.  So gifts of such seeds are gifts that "last" years.

You could even save seeds from your own heirloom plants, put them in attractive packets which you could also make yourself out of recycled paper - there are templates and instructions on various website.

Plant Labels

Gardeners need to identify what seeds they have planted in either pots or in the ground.  A great gift would be a set of these made from either plastic or wood.  Perhaps accompanied by a weather-resistant marker pen.

Watering Can

In my experience, watering cans can wear out, especially if they are left outside or used a lot.  Some can rust or the the screws attaching the handle can fall out.  Plastic watering cans suffer from sun damage and have a limited life.   Most gardeners find that having more than one is very useful.  Look out for good quality examples or those that are decorative.  Or you could paint designs on one yourself.

Insect hotel

These creations, also called insectaries, provide somewhere that beneficial insects can shelter in the garden can serve as a garden decoration as well.  If you don't know about them see our article which also shows some different designs.   You could make one like the example on the right, yourself - from a strip of heavy duty fabric e.g.  shade cloth, with pieces of hollowed out wood packed inside.  Bamboo is a useful material since it already has hollows, but it is easy to drill holes in other materials. Providing insect shelters like this are a great way of keeping control of the nuisance bugs.

There are also designs that provide shelter from harsh weather (wind and rain) for butterflies.  They usually have long vertical slits instead of round holes.

Such "hotels" are also available commercially - just do a web search.  But it is worth reading up a bit on good design and materials to use.  Since SGA's article was written, these "hotels" (also called insectaries) have become quite popular and there is some excellent online advice on how to maximise their insect-friendliness.


Shelter for bigger critters could also make an excellent gift.  They can offer places for birds, microbats, ringtail possums or sugar gliders.  There are different designs for the different animals and birds.  You'd best check out what creatures are in the area and, of course, if the recipient want those creatures in their garden.  Check out some advice here.

Compost bin or worm farm

Since compost bins or worm farms are excellent ways of turning waste into "black gold" for the garden, they make wonderful gifts.  Of course, check first if your recipient has one already.

Tools or Clothing

There many garden tools which gardeners need.  Giving them as gifts mean you can buy higher quality than gardeners might for themselves:

  • secateurs
  • lopper for difficult pruning branches thicker than those that secateurs can cut
  • a really lovely and long lasting stainless steel hand trowel or hand fork
  • long lasting scratch-proof garden gloves
  • pruning saw
  • knee pads that strap on
  • too carrier - either a tool belt/apron to wear around the waist or a caddy to carry.

Other Ethical Gifts

If your special person is not a gardener but you are, there are a number of other gift items that have reduced environmental or social impacts.  There are now - at last! - dozens of ethical gift opportunities.  These include:

  • soaps and hand wash made from natural or organic materials
  • fair trade products
  • organic food products e.g. natural honey

Reusable Beeswax Food Wraps

This is an idea that particularly attracted our attention.  These food wraps are a colourful, durable, washable alternatives to plastic bags for packing snacks, sandwich lunches or fruit for the person on the go, and can also be used for storing food in the fridge or pantry.  Available from several manufacturers, they are usually made from organic cotton and coated with beeswax blending with natural resins.  There is even online advice on how to make your own.

Enjoy making or buying these gifts for your special people!!

New Book "Tomato"- All Your Questions Answered and More

Tomato – Know, Sow, Grow, Feast, 2018

This new book by Penny Woodward, Janice Sutton and Karen Sutherland makes a major contribution to providing tomato-lovers with all you need to know to choose the right varieties of this wonderful fruit, to grow them and to use them.

A request by Margot White of the Royal Tasmanian Botanic Gardens to Penny to write a book about tomatoes for the 200th anniversary of the gardens was the initiator of this book. Margot and Friends of the gardens collected and grew tomatoes from all over the world with assistance of tomato groups and breeders. The resulting collaboration between her and the three knowledgeable authors has yielded a book replete with information and hundreds of beautiful photographs of all types of tomato, with a special emphasis on heirloom varieties – and the book covers 223 of them!  Photos also illustrate every section of the text from sowing, planting, the different varieties to pests and growing problems.  And the photos accompanying the many recipes will inspire you to try different ways of tempting your palate.

If you wish to choose heirloom tomatoes to grow, you could choose them on the basis of their benefits to health, their appearance, your local climate characteristics or what recipes they are best suited for. There are red, pink, yellow, orange, white, green, purple and brown, blue/black or striped, blushing or swirls.

For some, particular health benefits may dictate choice - the higher dietary intakes of the chemical that gives tomatoes their red colour, lycopene, is associated with reduced risk of prostate cancer and cardioivascular health. The yellow colour of yellow tomatoes is partly a result of their lutein content and is known to help slow development of cataracts and macular degeneration and may be important in maintaining cognitive function as we age. Lutein is also present in orange and green tomatoes as well as some other yellow or green vegetables.

And then you might choose varieties because they are particularly suitable for certain culinary uses.

The different heirloom varieties are all described in terms of their appearance, flavor, history and sellers of seed (some shown in the image on the right) . There is also a handy guide to varieties suited to particular climates, withstanding disease or to the growing space you have available.

The section on growing tomatoes covers soil preparation, sowing, transplanting, spacing, pruning, grafting and water and fertilizer needs. The authors have provided an extract for SGA from pages 19 – 21 on liquid feeds. Here Karen Sutherland lists a range of options – some of them might surprise you! Those suitable for vegans are shown as V:

“Liquid feeds provide an immediate benefit to your plants and are useful as an adjunct during rapid growth stages, or when flowers and fruits are forming, to more slowly released nutrients already in your soil. They also improve soil microbial activity, helping plants take up nutrients more successfully. It’s best practice to water soil before and after applying any fertiliser, including strong liquid feeds. If making homemade liquid feeds in a plastic rubbish bin or bucket, ensure your container has a close-fitting lid to avoid mosquitoes. As a general rule, all homemade liquid feeds should be diluted to the colour of weak tea before using.

Worm tea – Also called worm wee and worm leachate, this is made from the liquid that drains out of the bottom of worm farms and will reflect the quality and make-up of what is fed to the worms. Dark brown in colour when it first emerges, once diluted it is safe to use on plants and highly beneficial.

Compost tea – Mix compost, water and molasses, and then aerate with an aquarium bubbler for three days. Due to the bubbler, the container holding this mixture does not require a lid. Put the compost inside an old pillowcase to avoid blocking the bubbler. The aeration multiplies natural microorganisms in the compost, resulting in a liquid that supplies nutrients and also improves soil microbial activity. Use ½–1 part compost to 4 parts water and a teaspoon of molasses per 4L of tea. V

Liquid seaweed – Although not a complete fertiliser, as it’s low in nitrogen and phosphorous, liquid seaweed contains valuable trace elements (iodine and potassium) as well as growth stimulants. It’s a great tonic to encourage plant growth and thicken plant cell walls, giving plants greater resistance to the extremes of heat and cold now so common in our altered climate. Use every two weeks and at transplanting to help with transplant shock. V

Fish emulsion – Generally contains a NPK ration of 5-2-2. Can be applied fortnightly and mixed with seaweed solution. Check labels for appropriate rates, and apply when soil is moist so that nutrients are accessible to plants.

Homemade weed teas – These can be made from the weeds you clear from your own garden. Fill your container loosely with freshly pulled out weeds, and cover with water and a lid. After three days, most nutrients will have gone into the water and the weed tea can be used. Strain the liquid into a watering-can, and use diluted to fertilise tomatoes weekly. This allows the nutrients in the weeds to be retained on-site and used in the garden more quickly than if the weeds were added to compost. It also allows the nutrients in perennial weeds to be used rather than lost to green bins. Rotted weeds can be added to your compost after using the tea, although perennial weeds may need an additional soaking to ensure they are rotted and can’t regrow. V

Specific weed teas – Some weeds have particular qualities that are worth introducing to your garden. The best plants for weed tea are those that have a long taproot and can seek out nutrients from deep in the soil. In permaculture, these plants are known as ‘dynamic accumulators’, as they store nutrients mined from the subsoil in their leaves; these nutrients can be made available to other plants through decomposition. Plants considered to be dynamic accumulators are comfrey, dandelion, nettle and plantain. V

Homemade manure teas – This enables the use of manures that would otherwise be problematic due to the weed seeds they contain, such as horse manure. If the tea is well made, the nutrients from the manure are retained, the weed seeds rot and the residue can be added safely to your compost. Tie the manure inside an old pillowcase to make a giant manure tea bag, and steep it in your container of water. After around three days, remove the manure to your compost and use a watering-can to distribute the manure tea on your garden bed, avoiding leaves.

Molasses – It’s not used for feeding plants directly, but because it promotes good microbial activity in the soil. This helps plants take up nutrients so they become healthier, stronger and more resistant to pests and diseases. Mix 100ml of molasses with a small amount of hot water to dissolve it, then stir the mixture into 10L of water and sprinkle it liberally over the soil. Use it once or twice per season only. V

Milk – Use it undiluted on the soil before planting, or added to compost to improve microbial activity, or utilise it as a foliar feed in the ratio of 1 part milk to 5 parts water. Studies on using milk to feed the soil are relatively new, but they show that approximately 1ml/m2 milk applied to soil improves crop yields and that raw milk may be the most effective. Certainly any milk past its use-by date in your fridge is better on your garden than down the sink. Skim milk is as effective as whole milk, and cheese-making by-products such as whey are also beneficial.

Banana skin tea – Lina Siciliano has come up with a novel liquid feed. Knowing that banana skins contain a lot of potassium, she reasoned that they could be made into a fertiliser by soaking them in water. She puts 20 skins into an old orange or onion bag, places the bag into her 10L watering-can, fills it with water and covers the opening. After 10 days, she uses the liquid straight (as long as it’s the colour of weak tea) or diluted, either weekly or fortnightly. Lina finds that her tomato plants flower better and grow tastier fruits when she uses this feed. V”

The extensive “Feast” section will delight both gardeners and cooks. It covers storage and preparation methods, how the varieties differ in flavor and texture, preserving methods and recipes for fresh tomatoes. As well as recipes for tomato sauce, pickles and sun-dried tomatoes, there is an excitingly large range of dishes where tomatoes are included with fish or other ingredients.  The soups such as Creamy Roasted Tomato + Squash, Bush Tomato or Tomato and Cherry Gaspacho sound delectable.  And you can even read how to make Bloody Mary and Tomato + Basil icecream!

Gardening the New Health App

At the combined 2018 SGA Annual General Meeting and the October meeting of SGA's Green Gardening Professionals, Paul West, well-known from the SBS TV program River Cottage gave an inspiring talk about gardening and how it can make us, and keep us, healthy.

Summer Series of Talks

Christmas is approaching, and SGA has a great gift idea for that special gardener in your life. Or maybe it’s a perfect gift to give yourself.

For the first time SGA is running a Summer Series of 7 gardening talks over 7 weeks. This series will kick start the gardening year and is for all gardeners, from novice to experienced. Attendees will come away with inspiration, new ideas and projects for the garden that will also help the environment.

Every Thursday evening at 7pm from 17th January 2019 to the 28th February 2019 we will be hosting a 45 minute talk followed by Q&A time and a cuppa, in the beautiful surrounds of Edendale Community Environmental Farm, Eltham.

The Summer Series can be booked as a package or as individual talks of your choice. If choosing an individual topic is too hard, why not buy a Gift Voucher and let the receiver of your gift make the choice?

We have worked out some very special Christmas Present prices for you.

• The complete Summer Series of 7 talks for only $122. A 30% Christmas discount
• A single talk for only $20. A 20% Christmas discount

The gift of a single talk makes a perfect small present or Kris Kringle gift.

Buying Tickets

Tickets can be bought at the Summer Series Booking Page. From the main booking page, you can buy tickets for the whole series, or if you only want to buy tickets for specific talks, you can link to the individual event booking pages pages via the headings for each talk.

Gift Vouchers

Gift vouchers can be purchased in any of the booking pages. The gift voucher link can be found near the top of the booking page, near the social media icons. You can choose the value of the gift vouchers and it will be valid for any SGA workshop or talk.

Sample Booking Page

What is on Offer

Full Summer Series Package - All 7 Talks over 7 Weeks - Thurs 17 Jan - Thur 28 Feb

This summer series is a great way to start the new year in the garden. Learn about growing healthy food without use of harsh chemicals - how to increase the biodiversity of your garden, inviting in birds and bugs and using indigenous plants.   About the food, fibre and medicine properties of some of our indigenous plants.  How to use water resources wisely, reduce waste and reuse materials in your garden.


Talk 1. Water Smart Gardening - Thursday 17 Jan 19

Water is critical to a garden’s success. As we experience hotter and dryer summers, we need to be mindful about how we use water still while helping our gardens to thrive.

In this talk Richard will discuss design, maintenance and watering options for you to consider at home that will help reduce water usage while  supporting a healthy and productive garden.

Talk 2. Garden Pests – A Dance with Nature -  Thursday 24 Jan 19

Your garden is the home for many types of insects – the Good, the Bad and the Ugly.

In this talk Richard will look at how to use nature to strengthen the balance within your garden allowing you to minimise unnecessary chemical use. We will discuss mechanical, cultural, biological and low impact chemical controls to help you manage your garden pest problems.

Talk 3. Attracting Birds to your Garden - Thursday 31 Jan 19

The variety of birds attracted to our urban gardens seems to be decreasing but there are some simple changes you can make to your garden to make it a more inviting habitat to visit.

In this talk Richard will discuss how to change your garden and invite birds to take up residence once again. He will cover the fundamentals of a habitat garden incorporating the important habitat elements of food, water, shelter and nesting places.

Talk 4. Indigenous Plants for Food, Fibre and Medicine - Thursday 07 Feb 19

The Australian bush provided the first nations people all the Food, Fibre and Medicine needed to thrive in this unique country.

In this talk Richard will introduce you to some of the local plants used by indigenous Australians and inspire you to grow them in their garden.


Talk 5. Preparing your Garden for Autumn Harvest - Thursday 14 Feb 19 - Valentine’s Day

While summer is at its peak and its too hot to go outside in the garden, spend some time  planning your veggie garden for the autumn harvest.

In this talk Nicole will cover autumn maintenance activities, what veggies to plant and how to help them produce a bumper harvest.


Talk 6. Garden Weeds – A Dance with Nature - 21 Feb 19

Weeds are the bane of the home gardener but also a serious threat to local native flora and fauna. Weeds compete with preferred plants for space, light, nutrients and water and often are designed to win the battle.

In this talk Nicole will cover identifying and control weeds using an integrated approach that minimises negative environmental impacts. She will also talk about edible weeds.

Talk 7. Thrifty Gardening – Reduce, Reuse and Recycle in the Garden - 28 Feb 19

Waste is a growing environmental challenge that we can all do something about. Remember, there is no waste in nature and we can apply this thinking to our own lives and gardens.

In this talk Nicole will inspire you to use more recycled materials in your garden, helping the environment while making your garden more beautiful, unique, functional and productive.

The talks will be presented by two of SGA’s passionate trainers.

Richard Rowe

Richard is a passionate home gardener, worm farmer, experienced trainer and community facilitator. After a long and successful corporate career in finance and sustainability, Richard now focuses on environmental education for both adults and school children and on the local food movement.

Nicole Griffith

Nicole is a qualified teacher with over ten years of experience as an educator and presenter. She has a particular interest in edible gardening and has worked with both school and community kitchen garden programs