Crop Rotation
Crop rotation – despite what my non-gardening mates believe, is NOT the twisting of sunflowers to chase the sun (although, they do have a point… they are crops, and they are rotating!). Crop rotation is in fact a method of managing plantings, both on a small (vegie patch) and large (farm) scale to minimise the risk of pests and diseases, and maximise the yield and productivity of crops. Yup, it all sounds terribly technical, but I promise you it’s not! Hey, if I can manage it, I reckon just about anyone can!
What’s the Deal?
The definition of crop rotation I like the most is ‘The successive planting of different crops on the same land to maximise soil fertility and help control pests and diseases.’ Okay, it sounds very agricultural, but, in essence, this is the principle that we, as home gardeners, can apply to our vegie patches. And let me tell you, it works. The top notch vegies that we grow in our yummy yards, almost always, remove many and various nutrients from the soil during their growing periods. That said, a number of them replace nutrients as well (think beans, peas and other legumes). By varying what we pop in the patch, and what type of crop follows another, we can ensure that our vegies get what they need from the soil… and we get what we need from our vegies!
The other benefit of rotating our crops is that the process helps to interrupt the cycle of host specific pests and diseases. This means that harmful pests and diseases are unable to build up to damaging levels either in the soil or on the host plants themselves. Crop rotation has ‘moved’ their favourite host plants from the area, perhaps whilst the pests were ‘resting’ over winter, and essentially they are now unable to breed or, if they do breed, they no longer have a food source for their young to thrive. Hence the cycle is broken! Hurrah!! Crop rotation is a common practice in many large scale agricultural endeavours, such as in the rice paddies in Southern China. Over a two year cycle, a rice crop is generally followed by an “upland”, non-related crop (such as sugar cane) to help break the cycle and infestation of rice borer. And it must work, cause these guys have been doing it for a long, long time! In fact, crop rotation is reportedly one of the oldest cultural practices that is still kicking around….early civilisations in Africa and Asia used it, as did the Romans.
So how do you do it?
Everyone and their gardening book has a different method for successful crop rotation. After much discussion in the SGA trenches, we have come up with a system we like a lot. It’s simple, easy to manage, and it works!
Our system works on a four bed rotation, meaning there are four separate planting areas. Don’t fret if your garden doesn’t seem big enough to cope with all these beds. You can instead have just one bed and rotate the produce each season. It may mean you can’t grow tomatoes every summer, but you’ll have fun with a lot of other vegies in between! Vegies you can trade for tomatoes at your local vegie swap. If your garden is large enough, use what space you have available, and divide this up into four separate “zones”. Or, if you are starting from scratch, consider a mandala circle style vegie garden. While they look amazing, they will also maximise space, and allow for the zoning of planting areas (which in turn makes crop rotation even easier!). You can even have a spot for the chooks!
The Four-Bed Crop Rotation System
Lets get down to the nuts and bolts of the whole thing… how to do it. Firstly, we need to know a little bit about plant families, because this is a key principle behind crop rotation. Essentially, each area should be planted with a different plant family each season (generally every six months), to help avoid any nasty pest and disease outbreaks. So, who’s related to whom?
Amaranthaceae
Beetroot family
Beetroot
Quinoa
Spinach
Swiss Chard
Cucurbitaceae
Marrow family
Cucumber
Zucchini
Melon
Pumpkin
Squash
Solanaceae
Potato family
Eggplant(Aubergine)
Peppers (Capsicum and chillis)
Potato
Tomato
Compositae (Asteraceae)
Daisy family
Chicory/Endive
Jerusalem Artichoke
Lettuce
Salsify
Umbelliferae (Apiaceae)
Carrot family
Carrot
Celeriac
Celery
Fennel
Parsley
Parsnip
Dill
Cruciferae (Brassicaceae)
Cabbage family
Broccoli
Brussels Sprouts
Cabbage
Cauliflower
Kale
Kohlrabi
Mustard
Oriental Brassicas – e.g. Bok Choy
Radish
Swede
Turnip
Leguminosae (Fabaceae)
Pea & Bean family
Alfalfa
Beans
Peas
Clover
Fenugreek
Lupin
Alliaceae
Onion family
Garlic
Leek
Onion
Shallot
Poaceae
Grass family
Sweet corn
Maize
The principle is that one family member shouldn’t be followed by another family member in consecutive seasons. For example, once the tomatoes, members of the Solanaceae family, have finished fruiting and been removed, this area should be planted up with a member of another family such as a peas from the Fabaceae family.
There is another reason for this type of planting sequence as well. We know that some plants are referred to as “heavy” feeders, while others are “light” feeders. By introducing a crop rotation system, we can estimate the potential levels of soil nutrients remaining in the plot and plant up accordingly. For example, the Brassiaceae family are mainly heavy feeders and will take a lot of nutrients from your soil. However the Alliaceae family are light feeders and will not do well in a rich soil. Therefore it makes sense to plants onions after cabbages! Sounds complicated? I promise, it’s not! Just think logically and you can’t go wrong!
With these principles in mind, a suitable four-bed crop rotation may look like this:
| Season One | Season Two | Season Three | Season Four | |
| Bed One | Legume | Heavy Feeder | Light Feeder | Green Manure |
| Bed Two | Heavy Feeder | Light Feeder | Green Manure | Legume |
| Bed Three | Light Feeder | Green Manure | Legume | Heavy Feeder |
| Bed Four | Green Manure | Legume | Heavy Feeder | Light Feeder |
Heavy Feeders include potatoes, tomatoes, cauliflower, broccoli, cabbage, sweet corn, lettuce, cucumbers, zucchini, spinach, lettuce and Asian greens.
Light Feeders include onions, leeks, garlic, beetroot, carrots, parsnips and silverbeet.
Legumes include peas, snow peas, broad beans, runner beans, snake beans which fix nitrogen.
Green Manure Crops are crops grown, not to be harvested, but to be worked back into the soil. These are generally comprised of thickly sown annual grasses and/or legumes, that are tilled back into the soil before they flower or form seed heads. They add nutrients during their growing period and organic matter to soil in veggie patches, perfect for getting the next seasons edible crop off to a good start! Many nurseries stock pre-packaged green manure seeds.
Keeping Track of the Patch
Like a lot of things, crop rotation works really well in theory, but can prove a little daunting, especially if you’re memory is anything like mine. The solution – a blackboard in the garden shed, or a gardening calendar, outlining what was planted in what patch during each season. This is a great visual reminder of what’s happened in your yummy yard, and will help you keep track of the rotations happening in your patch.
There really are no hard and fast rules when it comes to crop rotation, but, if you follow the four bed rotation above, and keep the following four tips in mind, I reckon you’re on the right track:
1. Don’t follow one crop with another from the same family
2. Don’t follow one heavy feeder with another heavy feeder
3. Do plant a green manure crop at least once in every 4 seasons to replenish your soil.
4. Do read the SGA fact sheets on individual plants when planning your next crops
Crop rotation may take a little bit of practice and patience to get right in your neck of the woods, but, once you’ve mastered it, it is as easy as 1,2,3,4!
Diverting Rubbish from Landfill: Recycled Treasures
“My garden is chock-a-block with rescued plants, rescued pots & garden furniture, mirrors, birdcages, wheelbarrows, barrel hoops, ladders and all sorts of other bits and pieces. Not only do I collect treasures from the hard rubbish and Op shops. My friends and work colleagues donate things too. Some are used ‘as is’, others are tweaked, tarted up, assembled or arranged to make them more useful or display-worth.” So says Tine Grimston, from Rowville, Victoria.
As well as using recycled treasures, Tine tries to be sustainable in other ways. She is a participant in the local council’s Garden's for Wildlife program and has fruit and nut trees, a veggie garden, water tanks, solar panels, indigenous and native plants and a pond.
She and her partner, Wayne, purchased their nearly half-acre property in 1993. The house was 3 years old, and the garden consisted of grass, several knee-high Hakeas along the back fence and a couple of pittosporums in the front. Starting the garden was a challenge. It was extremely wet during the first year so that venturing outdoors required gumboots and necessitated drainage works. Since then the main battles were drought, regular frosts in winter and spring and a soil structure of compacted clay and builder’s rubble. In summer, cracks in the ground large enough to put a fist into opened up.
With such a large area of lawn to mow the quantity of grass clippings was enormous. Thinking that there would eventually be garden beds along the extensive fence-line which was shared with six neighbours, they piled the clippings there to form the beginning of a soil improvement program.
As time went by, the grassed area has diminished with every new garden project. They wished to have pleasant views from all windows, so began with a garden bed along the fence-line that was visible from the living area. They planted out wheelbarrows with succulent cuttings, and started collecting old wooden stepladders to give height to a new garden bed. Five of the six fence sections have been replaced with higher fences in the last two or three years, so there is a further need to find ways to hide them. Concrete 
reinforcing wire rather than plastic lattice has been used and Ivy Leaf pelargoniums made a quick cover.
There is no overall design for the garden – it has developed in fits and spurts as time, money and inspiration have allowed. Influences were the need to incorporate some great gifts (the gazebo, a garden arch, two huge terracotta pots, new gates to 
replace the closed-in wooden ones) and some great roadside finds
(mirrors, birdcages, ladders, wheelbarrows, pots, garden furniture). Tine joined the Dibble and Hoe Garden Club about 10 years ago and the beautiful gardens of members have been inspiring. Plant swaps have been source material for much planting.
There is a large central lawn surrounded by flowerbeds to the north of the house. All the paths and garden beds have curvaceous, serpentine edges. The rear of the house faces west and gets the full afternoon sun. This part of the garden has a pergola draped with Wisteria and Bougainvillea to shade the windows, a pond, gazebo, circular veggie garden, 
potting and composting areas and a number of fruit and nut trees. The south side of the house has a curving sawdust path, with a ‘geranium wall’, a herb garden and additional fruit trees.
Pictures: Tine Grimstone
While most babies are cute, cuddly and adorable, this is definitely not the case for the offspring of the Black Sawfly Caliroa cerasi. The larvae, known to us as Pear and Cherry Slugs, are possibly the ugliest of all pests, and the mess they make to some of our favourite fruit trees is pretty unattractive as well!
Description
A beautiful deep, glossy black with a lighter coloured head, the Pear and Cherry slug grows to only 1cm in length and about 0.5cm wide. Mum is a Black Sawfly, a small, shiny, black wasp with a wingspan of 1 cm and a saw-like appendage with which she cuts leaves of the host plant to deposit her eggs.
Plant Damage
The female sawfly deposits her eggs in a small slit in the leaves of her favourite trees in spring. After about 2 weeks, the slug-like larvae emerge, munching the leaves to a skeleton. Heavy infestations of slugs can cause serious defoliation, and result in incredibly unattractive and unproductive trees. They drop to the ground where they go through the pupal stage allowing another generation of flies to develop. Slugs will appear in early summer, and, after the next lot of pupae have spent winter in the soil, again the following spring.
Plants Affected
Pears (incl. ornamentals), cherries (incl. ornamentals), plums, quinces, apples, hawthorns and crabapples.
What to Do
- Blast them off the leaves with a strong jet of water and then band the tree with a low environmental impact horticultural glue.
- Make a deterrent spray by collecting and squashing slugs and placing in a bucket of boiling water. Once this has cooled, spray this on the leaves (including the undersides) of affected trees and scare those slugs away!
- Some recommend dusting the leaves with wood ash, but since most of us don't have open fires to collect it from, try other powdery substances like chalk or flour. Talcum powder also works for some gardeners. Others have mixed fine builders' lime (about a large handful in a bucket of water). It won't dissolve so keep the sprayer agitated and remove any filters.
- Since sawflies pupate in the soil, adding wood ash - or even powdered lime - to the soil can help too. These substances may also benefit the soil if it is acid, but don't add too much.
- Get a couple of chooks to scratch around the base of host trees over winter – they can’t resist the pupae napping in the soil!
- Create a diverse garden. This encourages predators like other flies, lacewings and wasps and they will all attract insectivorous birds. Plenty of shrubs and herbs with many small flowers will be just the answer.
Photo: Sharron Pfueller
Designing Productive Gardens
Few things can be quite as satisfying as growing your own vegetables, herbs and fruit. The quality and freshness of home grown produce combined with the peace of mind of knowing which fertilisers and chemicals have been applied has become an important issue to many people.
Thoughtful planning before you plant can save you months or even years of wasted effort!
You may wish to develop a purely functional layout using formal beds and planting rows, or alternatively formulate a more integrated planting design, which combines vegetables, herbs, fruit and ornamental plants. Many techniques or philosophies ranging from organic gardening to biodynamics, permaculture, and companion planting have become increasingly relevant and popular with today’s home gardener.
Edible gardens don’t have to be large, even a few pots on a balcony are enough to grow herbs and veggies. With many dwarf varieties available, even the smallest space can be used to grow tasty food including fruit.
Garden Styles
It is important consider the type or style of garden you want before construction begins in earnest - and even draw it up on paper.
Kitchen Garden
This is a traditional walled, fenced or courtyard garden. The fences or boundary hedges can provide protection from wind and north or west-facing masonry walls can assist plant growth by holding daytime heat and radiating it at night.
Potager Garden
A more romantic, decorative vegetable garden which includes flowering plants - sometimes confused with the Kitchen Garden.
Permaculture Garden
An organic garden which uses Permaculture principles for fertility and pest and disease control mimicking the way Nature does things. Such a garden has less emphasis on aesthetics.
Free Style Garden
A combination of some of the above. In reality, it is this style which is most common. Most of us don't start from a cleared block of relatively flat land, and even if we do, we may want to include shrubs, trees and decorative flowers. It is possible to apply permaculture principles to some or all of your garden, or to enclose just a portion of the garden with a wall, fence or hedge. It is also possible to intersperse vegetable beds with beds of roses, dahlias, asters and the like and to grow flowering shrubs along boundary fences.
Choosing a Style
Factors that will affect your choice will include:
- Relative importance of appearance and gardening approaches
- If you like straight rows and regular squares or circles for your garden beds, a wholly permaculture garden is probably not for you. But you could still incorporate some aspects such as "use and value diversity".
- The amount of time available to devote to upkeep and maintenance
- If you are time-poor, just a few veggies and perhaps just a small number of fruit trees might be a good choice. An easy-to-care-for potager or structured kitchen garden can be achieved in either a small or large section of your land. See more at the end of this page.
- The amount of usable space at your disposal
- Steeply sloping land, building cover as well as the size of your "block" will be important in deciding what to plant where. However, it is possible to grow some produce on a small balcony or even inside the house.
- Growing habits of productive plants
- Most garden vegetables are planted on an annual basis (either for cool or warm season growth) however, many plants including rhubarb, guavas, artichokes, strawberries, cane berries and asparagus survive for many seasons and, along with fruit trees, should be considered as permanent plantings.
- The suitability of the available space in terms of soil and microclimate - see more below.
- How to include other useful plants
- There are many herbs that you might want for culinary use such as thyme, oregano, parsley, mint and rosemary. They have other important features too - their flowers are excellent for attracting bees and other beneficial insects which help in pollination or in controlling pests. Take care though with herbs which become invasive such as mints (including Vietnamese mint) and horseradish. They are best grown in pots.
- You might want some of the dozens of other herbs which have beneficial uses. For example, lemon verbena and lemon balm are useful for making teas and additionally provide colour, fragrance and attract insects. Other plants such as the wormwoods and scented geraniums can be useful in repelling harmful insects. Most of these can contribute to permanent plantings. In a potager style they could be grown as hedges to frame and protect the vegetable area.
Important Requirements
Soil
The soil forms the basis of a productive garden. It provides oxygen, water and nutrients to the plant roots, necessary for their growth. A productive soil should have good structure, be well drained, and be rich in compost and manure. If your soil is not like this you may need to postpone planting while you add compost, manure and/or grow some nitrogen-fixing crops such as mung beans, chick peas or lupins then cut them down and dig them in as green manure.
The addition of organic manures and compost is fundamental to the success of vegetables and fruit trees. Organic matter provides nutrients for plants as it is broken down by soil micro-organisms eventually forming part of the humus layer in the soil. This greatly improves soil structure leading to better drainage, oxygen availability, water retention and nutrient holding capacity.
A compost-rich soil is ideal for growing healthy vegetables. It will encourage a large worm population, supply ample nutrients, good soil structure and drainage. Composting is also excellent as it can recycle most kitchen leftovers as well as garden waste.
If your soil is hard clay or almost pure sand you could include raised beds by constructing edging and importing soil from elsewhere. Or no-dig beds or wicking beds could be useful alternatives.
Sun
It is important that fruit and vegetables receive sufficient sunlight for their growth requirements. Vegetables grow quickly and need sunlight for photosynthesis to produce the energy needed for this growth. Northern aspects are ideal for a produce garden with beds running roughly in a north - south direction. At least 4 to 5 hours direct exposure to sunlight a day is recommended for most fruit and vegetables. Some say 6 hours. But don't forget that there are some vegetables that don't mind shade.
Water
Regular watering is also essential for successful fruit and vegetable crops. Water is a precious resource so think about installing a rainwater tank or a grey water system which re-uses laundry water.
Rainwater may be limited by the season (i.e. summer) but grey water is available every time the washing machine is used! Water flow can be regulated to the garden by using soaker hoses or installing irrigation systems.
Mulch
Mulches play an important role in the produce garden. A layer of pea or lucerne straw mulch will retain soil moisture, protect plant roots from summer heat, return organic matter to the soil, keep fruits off the soil surface and reduce the incidence of weed competition. Sugar cane mulch can be used, but is not as useful in providing a little extra nitrogen.
Vertical Structures
Your garden will almost certainly have a boundary fence. It may also have walls of the house, shed or garage. Although they will produce shady areas, some will be really useful for supporting cane berries, passion fruit, chocos, grapes, pumpkins, kiwi fruit, cucumbers and tomatoes. Alternatively, your plan should consider how you will provide support for these edibles if you wish to grow them. For some, such as cucumbers, a movable or demountable support is useful since they are best when not be grown in the same place in subsequent years.
Remember too, that fruit trees can be espaliered on fences, but also on trellises which you could construct anywhere in the garden. Espaliered fruit trees are very productive and take up much less space in your garden.
Maintenance And Care
Planting times will vary for different vegetables, herbs or fruits depending on their growing seasons. Generally speaking warm season vegetables are planted out in spring and cool season vegetables planted in autumn. Fruit trees, vines and shrubs, and some root crops are planted in winter. It is essential to plan ahead and ensure space is available throughout the year for different annual vegetables.
The presence of weeds in produce gardens is undesirable. Weeds compete for valuable resources and may attract or harbour pests and diseases. Proper mulching of the garden will significantly reduce the weed load. However, you need to be prepared to spend some time removing those that continue to grow - and, if they have not gone to seed, perhaps composting them.
Pests and diseases are a natural part of the plant kingdom and it is not possible or desirable to totally eliminate them. Gardeners should aim to achieve a balance of pests and predators, in which pest numbers do not jeopardise crops, but still provide a food source for the predators such as birds, spiders and predatory insects. Healthy soils and sensible planting and watering also help reduce the incidence of pest and disease.
Crop rotation helps to maintain a healthy soil profile and minimises the transfer of disease from one crop to another. There are many systems of rotating crops, some based on the families that vegetable belong to, others based more on nutrient requirements. It is a good idea to periodically leave some areas fallow (nothing planted) or plant a green manure crop that is dug into the soil. Click here for more information.
Fruit trees, shrubs and vines will need periodic pruning. Most fruit trees will require summer and winter pruning to produce a good crop of fruit each year. The structural pruning is carried out in winter to form the framework of the tree. In summer, water shoots and upright branches are either pruned back or trained down horizontally, to encourage fruiting over stem growth.
Probably the most important factor in planning for a produce garden is to be realistic about the time you are able to spend on the garden once it is planted. We suggest that, for a successful garden, you need to spend a few minutes every few days to check on what is happening it it - after all it is alive! These frequent short visits will enable you to:
- Harvest vegetables, herbs and fruit.
- Check the health of the plants. Do not leave old fruit, vegetables and pruning material underneath the plants as these can harbour disease - compost this material, unless the plant has a disease.
- Monitor weed growth - and pull a few out.
- Check soil moisture.
- Do minor pruning to keep shrubs and trees in shape.
- Check if nets are needed to protect fruit or veggies them from birds, rats, possums (please use very fine netting which will not trap anything)
- Enjoy the fresh air, sunshine, the hum of insects and the songs of birds!
Josh Byrne - SGA Patron
SGA caught up recently with our patron, Josh Byrne, to hear how he became interested in sustainability, and what he’s up to with the team at Josh Byrne & Associates.
Josh has been a sustainable gardener since getting involved in his family garden growing up in coastal Western Australia. Josh had his own veggie patch, and looked after his dad’s extensive collection of herbs. He was committed to gardening without using herbicides and pesticides from the start, maybe inspired by his interest in the natural world and growing up on the amazing Esperance coast.
That commitment influenced Josh’s selection of subjects at high school and later at Murdoch University – he was fascinated by the natural world, and developing his understanding of how the built environment could work best in it.
Developing a career pathway
Josh ran a part time gardening round while he was a student. He continued developing his understanding of sustainable gardening, focusing on water conservation and coping with the sandy soils around Perth, with the aim of gardening better in a challenging environment.
While Josh was studying environmental science at Murdoch University, he lived in an old student rental house, where he and his mates developed a working, productive and attractive garden. Josh became attracted to permaculture principles and the importance of good design to achieving good outcomes. That, in turn, led to his involvement in a research group at Murdoch, working on environmental technologies for regional and remote areas.
Josh first appeared as a guest presenter on the ABC’s Gardening Australia nearly 20 years ago in 2 segments about his student garden. That led to an invitation to be Gardening Australia’s regular Western Australian presenter. At first he declined the invitation to pursue overseas travel, including working as a volunteer on a permaculture project in Africa, as well as spending time on a Kibutz in Israel learning about advancements in irrigation technology. He returned to Perth and eventually picked up the role where he demonstrates practical ways to create attractive, productive and water efficient gardens to a national audience. Josh is a regular contributor to the Gardening Australia Magazine and author of two best-selling books, The Green Gardener published by Penguin, and Small Space Organics published by Hardie Grant.
Working for sustainability and community engagement
Josh saw an opportunity to be involved in creating productive and attractive gardens, and educating people about how they could get involved. He established Josh Byrne & Associates which aims to deliver projects for sustainable communities with an integrated approach to landscape architecture, environmental engineering and sustainability, community engagement and communications.
Josh has recently been awarded a PhD from Murdoch University and is a Research Fellow with Curtin University’s Sustainability Policy Institute and the Cooperative Research Centre (CRC) for Low Carbon Living, and an Adjunct Associate Professor with the School of Civil and Environmental Engineering at the University of New South Wales. His research activities continue his early interest in urban design, particularly high-performance housing, water sensitive design and sustainable urban developments.
Josh consults to West Australian state agencies such as Water Corporation, LandCorp and the Metropolitan Redevelopment Authority on matters relating to urban water management, environmental technology and design and has contributed to projects around Australia. Josh’s interest is in doing urban design better. He’s looking at improving urban sustainability and water conservation with innovative, affordable, sustainable design and developing shared spaces, parks, facades and streetscapes so that as cities become denser, we develop a high quality public realm. On the Density by Design website, Josh seeks out the leading minds and ground-breaking ideas on sustainable higher density residential projects around Australia, that are inspiring change through demonstration.
In addition to design and development, nuts and bolts gardening is still a key activity, as is community consultation and involvement. One of Josh’s key interests is the responsible use of garden nutrients. In conjunction with the WA Department of Biodiversity, Conservation and Attractions River Guardians’ program and Water Corporation’s Waterwise program, he has developed and presents workshops providing Perth residents with the ideas and inspiration to create a successful garden while helping the Swan and Canning Rivers to stay healthy. The program included a personalised online assessment tool which aims to provide Perth residents with the knowledge and tools to create a successful garden without impacting the Swan Canning Riverpark.
The program is an example of how, as gardeners and community members, we all have opportunities to encourage councils and governments to incorporate great (and sustainable) shared spaces in urban areas, maybe to garden (sustainably!) a little or a lot, to reduce water use, recycle waste and use energy more efficiently. Environmental problems might seem so big that they are insurmountable, but we all have opportunities on our back or front door steps to contribute to the solution.
Josh is a recipient of the Australian Water Association’s WA Water Professional of the Year Award, and Murdoch University’s Distinguished Alumni Award for Science and Engineering. He is Patron of the Conservation Council of WA and Sustainable Gardening Australia, an Advocate for the national collaborative 202020 Vision urban greening initiative (a national campaign to increase urban green space in Australia by 20% by 2020) and an Ambassador for the Living Smart household sustainability program and Nature Play WA.
Virus or Variegation
A common error gardeners make is to assume that appearance of coloured areas on leaves is caused by natural variegation, fungal infection or nutrient deficiency. In many cases, the variegated colour of leaves of some shrubs, indoor plants, lettuces, herbs is a natural mutation. Happily, this is not a destructive mutation, but one that results in less chlorophyll in some parts of the leaves, causing a paler and mottled effect. Sometimes, keen gardeners have selected these plants and bred from them. These variegated plants can be lower in vigour and shorter-lived than their 'normal' relatives but this hasn't affected their popularity as garden plants.
Variegation Due to Plant Viruses
There is, however, variegation caused by some sort of plant problem. Although some garden pests, such as aphids can cause leaf yellowing, this colour change is not the only sign of an infestation. A more problematic cause of colour change is infection by disease-causing viruses or virus-like viroids and phytoplasmas, of which there are hundreds. Shown at the left is the leaf symptoms of cucumber mosaic virus (image courtesy of www.whitefly.org).
Fortunately, trees and Australian native plants have few virus disease problems and, interestingly, viruses in wild-growing plants don’t seem to develop disease, although they have not been studied as well as cultivated plants. It is in cultivated plants, mainly food crops, that virus infection is of most concern. Because viruses and virioids are very simple “organisms” with DNA or RNA coated by a protein layer. They cannot survive for long or multiply outside of a host so they are 'obligate parasites' - they can only increase in number inside a living organism. Once inside the plant, the plant is harnessed into producing more virus. The plant cannot grow properly because its energy and nutrients are diverted away from normal activities like photosynthesis.
Shown here are the leaf and fruit symptoms of tomato spotted wilt virus (images courtesy of North Carolina Co-operative Extension).
Virus infection may result in a variety of symptoms - leaf colour variegation (which may be mottling, stripes or sport) is just one. Viruses may infect all parts of the plant but symptoms are generally most obvious on young foliage. Some result in ringspots, such as ringspot virus on Cymbidium orchids; bronzing, such as that caused by tomato spotted wilt virus; malformations, as caused by potato leafroll virus; and wilting, also caused by tomato spotted wilt virus.
Classification
It is common practice to use the common name of a virus, rather than its scientific name (unlike the use of botanic names of plants). Viruses are named based on the first plant on which it is studied, followed by the most obvious symptom of the disease on that plant, followed by the virus group to which it belongs. For example, apple mosaic virus is the common name of the apple mosaic ilarvirus, and tulip breaking virus is the common name of the tulip breaking potyvirus. Many viruses have a wide host range, not just the plant it is first studied on, and the symptoms can vary.
Spread
Seed
Plant viruses, like those infecting humans and other animals are spread by some sort of contact. More than 20% of virus diseases are spread via seed where the virus is mostly in the cells required for growth, but some are in the seed coat.
Vectors/Carriers
Some are spread by vectors such as aphids and thrips. Shown here is rose mosaic virus. This is likely to be spread by aphids (image courtesy of The Utah Department of Agriculture and Food, Division of Plant Industry). Some are carried by single celled organisms such as Polymyxa betae which transmits Beet necrotic yellow vein virus by infecting plant roots.
Sap
If plant leaves become damaged by cultivation or animals feeding, sap containing virus may be transmitted another plant. This has been observed with cucumber mosaic virus.
Other
Although rare, nematodes and fungi are also implicated. Parasitic plants can spread viruses. Tobacco mosaic virus can even survive in dead infected tobacco leaves in cigarettes.
All virus diseases will be transferred from infected parent plants through new bulbs, corms, tubers, stolons, and cuttings.
Control
As we know from human virus epidemics, animal viruses are almost impossible to control except by avoiding exposure, mounting our own immune system to fight off the infection or by vaccination. Plant don’t have the same options - once a plant is infected it remains infected. Some viruses do not infect the growing tip of a plant (the meristem) and this is often used to advantage by growers. The unaffected tissue from the meristem of a plant can be tissue-cultured and can result in virus-free plants.
There are no chemical or biological controls.
So prevention is the only effective control. Methods include:
- Removing infected dying plants and destroying them so that vectors such as aphids do not spread the virus to healthy plants.
- Keeping weeds away - they can host viruses, so keep the surrounds weed-free.
- Paying attention to your own hygiene because some viruses can be spread by handling, so hand-washing between plants can be a necessity.
- Sterilising pruning and cutting implements after every plant or plant group – dip or wipe tools with methylated spirits
- Growing disease-resistant varieties - many resistant varieties of crops of economic value have been developed.
- Insect -proofing greenhouses. Professional growers often rely on insect- proof greenhouses to keep out possible virus-carrying vectors.
- Quarantining plants for suspect locations.
There are many virus diseases not yet in Australia, so quarantine is an important method of preventative control. Please adhere to quarantine legislation - you never know what a plant or seed might be carrying.
The Benefits of Indoor Plants
On average, every Australian spends around 90% of their time indoors, be it at work, at home, at the shops or the local pub - a figure that is quite astonishing. But, if you think that’s frightening – a number of studies have found that the air indoors (where we spend most of our time) is generally more polluted than the air outside (where we spend about 10% of our time - or even less in some months)! Having plants growing indoors is an easy and attractive way of cleaning up this pollution.
A class of chemicals called Volatile Organic Compounds (VOCs) are the main indoor air pollutants. VOCs are present in many common office and indoor items including carpets, paints, wall panels, wood products (especially particle board) and furnishings, and can be pretty bad news. Including such baddies as formaldehyde, benzene, xylene, and toluene, VOCs decrease the indoor air quality and are a significant contributor to “sick building syndrome”, a term used to describe a range of symptoms thought to be caused by the office or home environment. Carbon dioxide and carbon monoxide also pollute indoor air.
The CSIRO estimates that the health cost of poor indoor air quality could be as high as $12 billion annually1. Indoor plants reduce the losses occurring through increased absenteeism and reduced productivity in the workplace.
If that happens in workplaces, just think of what happens at home!
How Plants Protect People
Plants indoors can significantly reduce both VOCs and carbon dioxide from the air, meaning cleaner, greener, happier and more productive homes and offices2. But how do they do it? Removal of VOCs from the air indoors is actually done by the plant as well as the millions of micro-organisms in the soil. It has been shown that potting mix alone was able to remove some level of VOC’s from the air, although the amount removed significantly increased with a plant in the pot (due to the increased level of soil microbial activity that comes with having a real plant in the pot)2. Having just three indoor plants in 10m² of office space can go a long way indeed to improving indoor air quality.
When 28 different plants were compared the most efficient at removing VOCs were Hemigraphis alternate (red flame ivy), Hedera helix (common ivy) Hoya carnosa (porcelain flower or wax plant) and Asparagus densiflorus (foxtail fern) had the highest removal efficiencies for all pollutants; Tradescantia pallida (“wandering Jew”) was able to remove all but one of the VOCs tested 3. Don’t think, though, that these are the only effective plants (and don’t plant them outdoors as they become weedy). Those findings show that there are differences in plant effectiveness and suggest that it would be wise to have a mix of different species.
And in modern buildings with windows that are sealed to minimize unwanted temperature changes (“tight buildings”) levels of carbon dioxide are also higher than outdoors4, coming from air we breathe out, and can cause restlessness and sleepiness. Carbon monoxide can also be a little higher, generated by heating, smoking, incense and candles4. Since plants are responsible for removing these gases from the air, having them indoors not only helps save the planet, but helps make us less lethargic and generally feeling better!
Some research suggests that indoor plants, either because they bring people in contact with nature or because they improve indoor air quality can also increase creative task performance and lift mood.
So, let’s have a look at some readily available indoor plants, their light requirements, and their ideal positioning in the home or office.
Indoor Plant Care
Just like their friends outside, indoor plants need proper care because they can suffer from a variety of issues that can affect their health, well-being and appearance.
Too much “love”
This is the most common affliction of indoor plants. Yes, that’s right; many of us kill our indoor plants with love, either by overwatering or overfeeding them.
Feeding
Indoor plants are best fed once per month in the growing season or if flowering and then almost not at all during autumn and winter. However, this depends on what you feed them.
Watering
Watering needs to be monitored at all times. One of the best ways to do this is by putting your indoor plants into a self-watering pot, one that regulates the uptake of water into the soil. This way, over and under watering are no longer issues, and indoor plant ownership becomes a far less stressful endeavour.
Cleaning
It is also recommended that the leaves of indoor plants are periodically wiped with a damp cloth, on both the upper and lower surfaces. This helps remove dust that can build up and clog plant pores, removes any insects or eggs that may be present, and keeps the plant foliage looking shiny and healthy. It might be a bit tedious, but is worth it in the long run.
Light exposure
Rotate your plants every now and then (yes, turn them around on the spot) to keep growth nice and even by giving them even access to the source of light. Keep an eye on your indoor plants, especially over winter, as potential pest problems can present themselves in the cooler months.
Are there any downsides?
Unfortunately, indoor plants can be extremely harmful (often fatal) if ingested by pets, so it is advisable to keep indoor plants out of reach of puppies and kittens especially, but also adult dogs and cats.
References
1. Wood RA, Orwell RL, Tarran J, Torpy F, Burchett M. 2008. Indoor plants: improving the indoor environment for health, well-being and productivity. ISHS Acta Horticulturae 790: VIII International People-Plant Symposium on Exploring Therapeutic Powers of Flowers, Greenery and Nature.
2. Wolverton BC, Wolverton JD. 1993. Plants and soil microorganisms: Removal of formaldehye, zylene and ammonia from the indoor environment. Journal Mississippi Acacemy of Sciences 38 (2): 11 – 15.
3. Dong Sik Yang, DS, Pennisi SV, Son K-C, Kays SJ. 2009. Screening Indoor Plants for Volatile Organic Pollutant Removal Efficiency. HortScience 44 (4) 1377 - 1381.
4. The Centre for Australian Weather and Climate Research. 2010. Indoor Air Project Part 1: MAIN REPORT. Indoor Air in Typical Australian Dwellings.
A Pathway to Sustainable Gardening
There are many prompts that lead people into wanting to get into gardening and grow their own food. One of SGA’s enthusiastic volunteers tells us of her pathway into sustainable gardening.
“I lived in a high-rise apartment in Hong Kong for 26 years until I came to Australia. Apple trees were in the fairy tale books and vegetables were in the supermarket aisles.Read more
Choosing Fruit and Vegetables to Grow or Buy Organic on a Budget
If it is important to you to reduce your exposure to artificial chemicals in food, it can be quite expensive to buy organic fruit and veggies and it may not be possible grow all of them yourself. Production that is Certified Organic, means that as well as not being exposed to residues of chemical pesticides and herbicides, you are doing something for the environment because farmers and gardeners are not permitted to label food “Organic” if they use artificial fertilisers. But if you are on budget, like most of us, how do you decide which organic foods to prioritise when you go shopping or which to grow yourself?
This is not a straightforward task since knowledge of which fruit and veggies have most contamination is incomplete and fraught with controversy.
Health Issues
Eating organic food is believed to be better for our health. However, there is not agreement about this - some studies indicate higher levels of anti-oxidants in it but others find little difference between organic and conventionally produced food. Some argue that even with slightly higher levels of anti-oxidants in organic produce, the amounts are insignificant compared to overall levels we consume if our diets are rich in fruit and vegetables.
Artificial Chemical Residues
There is also debate about levels of chemical residues. Every few years, the United States' non-profit organization, the Environmental Working Group publishes the Dirty Dozen – a list of fruit and veggies with the highest residue levels. A new list was published this April. It was based on results of more than 38,800 samples published by the US Department of Agriculture and the Food and Drug Administration. They found that almost 70% or non-organic produce was contaminated with pesticides.
As in some previous years, strawberries top the list with most contaminated samples - one sample had 22 different pesticides. Next were spinach, nectarines, apples, grapes, peaches, cherries, pears, tomatoes, celery, potatoes and sweet bell peppers.
The Clean Fifteen – samples with least pesticide residue – was topped by avocados (only 1 pesticide found in any of 380 samples), followed by sweet corn, pineapples, cabbages, onions, sweet peas (frozen), papayas, asparagus, mangoes, eggplant, honeydew melons, kiwi fruit, cantaloupes, cauliflower and broccoli. Only 30% of broccoli samples contained residues.
However, critics claim that:
- The EWG is a political lobbying group for the organics industry so their results are not to be trusted
- EWG studies are not representative since samples come from different regions of the world where farming practices vary
- Amounts found were within “safe levels” determined by the EPA
- Pesticide residues can also be found in organic food
- The results do not agree with those conducted by independent scientists
So avoiding the Dirty Dozen might not be the way to choose which to buy organic.
How Do We Interpret This?
I think the answer is “with difficulty”! And it is even more difficult if we are in Australia or a country which obtains fruit and veggies from regions different from those supplying the samples used by the EWG where pests and pesticide use may be different.
In Australia, chemical residues in fruit and vegetables are regularly monitored and, according to Food Standards Australia and New Zealand, the allowed levels of chemicals are defined such that they are much lower than levels that might affect health.
However, there are very low levels of chemicals in many fruit and vegetables. And, unfortunately, no studies have been done to show that diets which contain "safe" amounts of a considerable number of different chemicals over a long period of time are safe or harmful. And it is highly unlikely that there ever could be such a study because a very large number of participants who either ate conventionally grown or organically grown produce would be required – and even then, it would be extremely difficult to prove that any observed differences were due to just to their diets.
So many of us prefer take the risk-averse approach and avoid chemicals altogether.
Reduced Environmental Impacts of Organic Produce
Another reason for choosing organic is that conventional farming uses artificial fertilisers. Manufacturing the sources of nitrogen in these involves fossil fuels and, therefore, greenhouse gas emissions. Such fertilisers are often applied in excess and that which is not taken up by plants runs into streams and rivers causing pollution which may cause algal blooms and damage to aquatic life.
And, of course, most pesticide use is not specific for particular pests and is able to cause unwanted effects on beneficial insects such as honey bees and natural predators.
The fuel usage (and associated greenhouse gas emissions) of transporting produce long distances, sometimes across the country, can also be considered. And they may be high for both organic or conventionally grown fruit and veggies. So if purchasing organic produce is not feasible, buying from local farmers’ markets or joining local food swaps still helps reduce this type of impact.
So What Criteria Could We Use?
Maybe we could think about this in a different way. One suggestion is to choose organic or grow your own for those with a large surface area e.g. broccoli, chard, spinach and celery, since the chemicals are mostly on the surface.
Another is that there is less risk of consuming any contaminants with fruit and veggies where we don’t eat the skin e.g. melons, avocado, citrus, shelled peas.
But what about carrots and other root vegetables? The skin contains valuable nutrients and fibre, and nutritionists recommend that we eat the skin. But the skin also contains more chemicals than the inside. The Centre for Science and the Environment (a public interest research and advocacy organization) has shown that thorough washing of fruit and vegetables will remove most chemicals. For root vegetables, scrubbing with a brush under water would be appropriate. But choosing organically grown root vegetables or growing your own would be more certain.
Then if environmental impacts are considered, buying organic or growing your own would be most useful for crops that have high nitrogen requirements such as sweet corn, brassicas, and leafy green vegetables. Or if neither of those is possible, then sourcing local food is still of benefit.
So you might choose to buy conventionally grown produce that has inedible skins - perhaps from local sources, and to focus organic purchases and growing your own on those that are most likely to be contaminated when conventionally grown or to have been transported long distances.
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