What are Pesticides?

Pesticides include insecticides, herbicides and fungicides, which are designed to kill insects, weeds and diseases respectively. Using pesticides may be necessary at times, but in many cases there are alternatives that are often more effective in the long run and less harmful to you and the environment.

Pesticides in the environment

What happens to pesticides released into the environment is not always known. They are either broken down or degraded by sunlight, water, other chemicals or microorganisms such as bacteria or remain unchanged in the environment for long periods of time. Some pesticides are selective against a given pest, while others are relatively non-selective towards a large group of organisms. After applying them to plants, pesticides can eventually end up in other parts of the environment, such as water, soil or air where they may affect other organisms.

Pesticides in our waterways

If a pesticide is very soluble it is easily transported by rainwater as runoff. Water from rain carries pesticides from lawns and gardens into nearby street drains. Street drains feed directly into waterways. Once in the water, pesticides dissolve, dilute or combine with other chemicals to create harmful combinations that can kill fish, frogs and aquatic life, limit beneficial plants and animals and increase growth of algae. Excess algal growth causes light deficiencies for plants and depletes oxygen levels that fish need to survive. Clean water is an essential part of our quality of life. We can help protect our rivers, streams, lakes and bays by rethinking and reducing our use of pesticides.

Pesticides in the air

Pesticides that are more volatile have the ability to evaporate and be absorbed into the atmosphere potentially moving long distances. Fine mists of pesticides can drift to nearby plants and kill them. Bees and other pollinators can be killed if a pesticide is sprayed when they are in the field. Pesticide sprays can also kill the natural enemies of pest insects. In the United States EPA studies on animals have shown that of the 34 chemicals that make up 95% of lawn pesticides, 10 are carcinogenic, 12 cause birth defects, 20 are neurotoxic, 7 alter the reproductive process, 13 cause liver damage, and 29 are irritants.

Pesticides in the soil

Pesticides that percolate through the soil may inadvertently kill beneficial organisms such as earthworms. They may also enter the groundwater and potentially pollute our drinking water. Pesticides are made to be toxic. These chemicals may affect your health, the health of your neighbours and the health of smaller animals and plants in your community. Be an informed consumer and use environmental common sense when using pesticides in your home and garden.

As a member of Sustainable Gardening Australia we ask you to consider chemical alternatives or use low environmental impact chemicals, slow release fertilisers and use only the amount recommended by the manufacturer. Try not to apply these chemicals before rain or on windy days.


Lead Contamination

Lead is an extremely stable element that is categorised as a heavy metal. It is a dangerous neurotoxin to humans and animals.

Small amounts of lead are naturally present in the soil and in vegetables, and should not cause alarm. This is generally in the range of 15 to 40 parts lead to one million parts soil (ppm).

Through the addition of industrial lead pollutants, such as lead particles and chips from lead-based paints, automobile emissions from leaded fuels, and other industrial sources, lead levels in contaminated soil range from 500 ppm to over 3,000 ppm.

Soils near a busy road are typically 30 -2,000 ppm higher than soils in a natural area. Soils adjacent to houses painted with exterior lead based paint may contain lead levels as high as 10,000 ppm.

Once soil has become contaminated with lead, which is not biodegradable, it remains a long term source of lead exposure.

Impact on Fruit and Vegetable Growing

Vegetables can absorb excess lead from highly contaminated soils. Planting a vegetable garden where rubbish was once dumped; on previous agricultural land; where there are nearby mines or smelters; or where a house once stood (the concern here is primarily from lead-based paints which were used prior to the 1950s), could all pose a hazard.

You can have your soil tested if you are concerned, but it can be costly (visit the website www.nata.asn.au ).

CSIRO has found more pollution in leafy vegetables and root crops than fruiting plant produce (for example, fruit trees, tomatoes, and peas and beans). This means that soils with more than 3000ppm lead are deemed ok for fruit and grain crops, but not for leafy or root vegetables.

Vegetable gardens should be established away from busy roads - at least 20 to 80 metres away.

If you're concerned about lead in your soil, consider taking these actions:

  • Peel root crops, such as potatoes and carrots, as most contaminants taken up from the soil are found in the skin of these plants.
  • Wash vegetables thoroughly. Discard older, outer leaves which absorb more lead.
  • Maintain a soil pH of 6.5 to 7.0 and provide adequate phosphorus fertilisation to reduce lead uptake from the soil.
  • Plant fruiting vegetables instead of leafy or root crops which take up more lead.
  • Organic matter added to the soil helps tie up lead and makes it less available to plants.
  • Mulch the soil to reduce blowing dust and to increase water retention.

Children and Lead

Lead poisoning is one of the most common paediatric health problems in the United States. In 1985 the U.S. Center for Disease Control (CDC) defined childhood lead poisoning as occurring at blood lead levels of greater than 25 ug/dL. This definition was revised down to 10 ug/dL, due to new scientific evidence showing decreased intelligence and slower neurological development of children with blood levels as low as 10 ug/Dl.

Leaded petrol was banned from sale in Australia in January 2002 and since then lead pollution from the air has been declining.

Improve your Diet

A CSIRO study in 2003 found that a major pathway for copper, lead, cadmium, arsenic and DDT is through the foodchain. A poor diet that is low in iron, calcium, calories, protein, zinc and vitamin C, and high in fat, will increase the risk that you will absorb lead from your diet.

A further study documented how much some plants tend to take up heavy metals such as lead:

High uptake: lettuce, spinach, carrot, endive, cress, beet and silverbeet leaves.

Moderate uptake: onion, mustard, potato, radish.

Low uptake: corn, cauliflower, asparagus, celery, berries.

Very low uptake: beans, peas, melon, tomatoes, fruit.

Soil Conditioners

It's almost impossible not to mention these two topics in the same breath! A great deal has already been written about both, but it is still worth remembering that mulch is the most effective way to keep moisture in your soil. You can choose from a wide range of mulch materials, but remember that it is very important to apply a generous deep layer of mulch.

Don't be tempted to spread it too thin. If your garden provides you with lots of prunings throughout the year, invest in a shredder and make your own supply of mulch to add to your garden - the ultimate in garden recycling! Mulching also acts to supress weeds, keep soil temperature stable and stimulate microbial activity, meaning less work for gardeners. Mulching should be considered an on-going soil conditioning process, and is as essential in the garden as pruning and weeding.

Natural Soil Improvers

Generally speaking, plants grown in a healthy, well-balanced soil will have an increased resistance to disease. A good garden soil is one that comprises approximately equal parts clay and sand and has a high proportion of humus and organic matter distributed throughout.

Natural Fertilisers & Soil Conditioners

N = Nitrogen, P = Phosphorous, K = Potassium

Compost N.P.K. 1.4-3.5 : 0.3-1 : 0.4-2

Well made compost that contains a large number of ingredients from many different sources will have adequate amounts of most essential major and trace elements. Compost, combined with any animal manures produces the best and safest all purpose fertiliser, containing both major and minor elements.

Animal Manures

Cow: N.P.K. 0.2-2.7 : 0.01-0.3 : 0.06-2.1
Sheep: N.P.K. 1-3 : 0.1-0.6 : 0.3-1.5

All animal manures provide valuable sources of nutritional elements for plant life. When combined with compost as part of the composting process, the final material provides the best all purpose fertiliser. When using manure straight on the garden, care should be taken that it is not too 'hot', i.e. that it has been broken down or weathered sufficiently. Use of composted manures eliminates smells and provides five times the nutrition as fresh manures.

Fowl Manure: N.P.K. 4-8 : 1.1-2 : 0.8-1.6

Is very high in nitrogen and phosphorus. Therefore, care must be taken that it is well rotted or composted before applying it to the garden.

Dynamic Lifter: N.P.K. 3.2 : 2.6 : 1.3

An organic general fertiliser based on chicken manure, which is fully processed and sterilised. It is suitable for every feeding situation and application encountered by the home gardener. It is easy to use, non-burning and impurity free. It slowly releases nutrients into the soil as it breaks down.

Blood & Bone: N.P.K. 4.5 : 5 : 0

An excellent nitrogen and phosphorous fertiliser with a relatively high percentage of both major elements.

Hoof, Horn, Hair & Feathers: N.P.K. 11-13 : 0.3 : 0

An excellent slow release high nitrogen fertiliser.

Bone Meal & Ground Burned Bones

An excellent source of phosphorus.

Seaweed Extracts: N.P.K. 0.5 : 0.1-0.2 : 0.1-1.9

There are several commercially available liquid fertilisers on the market, which are very beneficial, particularly for establishing plants and as a tonic for unhealthy plants.

Fish Emulsions N.P.K. 9 : 2 : 6

These are organic liquid fertilisers.

Comfrey leaves

An excellent source of potassium. Use wilted leaves under grass clippings as a mulch around fruit plants. It also makes an excellent compost activator.


A naturally occurring alkaline rock. It is a compound of calcium and magnesium carbonate and excellent when used to neutralise acid soils.


Used to break up the solid mass of clay into a more crumbly structure that can be worked on with compost, mulches and other high humus content materials. Gypsum also contains lots of calcium and sulphur, which are two major plant nutrients.

Wood ash

Scattered in layers in the compost heap, they will do the job of lime in "sweetening" the whole mass.

Leaf mulch

Although leaf litter is not high in nutrients, it has a very important role in the garden, creating within the soil a crumbly (friable) texture, which allows good water retention without water logging. Wherever there is leaf mulch, earthworms will abound. The more worms, the healthier the soil, which is one of our most important natural resources.

Don't Get Too Wet!

Whatever your soil type, good drainage is essential for healthy plants. Of course, if you have light sandy soil, the drainage is probably too good! This is where the use of compost will greatly reduce rapid moisture loss, and improve the soil's capacity to retain water, which is really important in these times of water restrictions. Heavy soils also benefit from this process, but some gardens may need more work than others! If you have a brand new house and a bare block of land which only offers compacted clay and subsoil, don't lose heart; compost can help!

Don't be tempted to plant straight into compacted clay, as very few plants are tough enough to handle it. Compacted fine clay particles don't allow water to drain away, so winter rains will cause the roots of plants to rot, and the hot summer sun bakes the clay as hard as concrete! Adding compost and mulching will help improve this soil, allowing water retention and drainage as the organic matter breaks down and mixes with the heavy clay soils.

In addition to a composting and mulching routine, some people opt to import new topsoil into their gardens. The best type of topsoil is a dark sandy loam, rich in organic matter to hold moisture but with enough coarse particles to allow good drainage. So if you need to buy topsoil, this is a very good investment. An important tip when establishing new garden beds is to avoid compaction of the topsoil before planting, although it is important to rake the soil evenly to ensure removal of air pockets. The soil will settle naturally, especially after watering, so you may even find it necessary to 'top up' the levels with extra soil after a few days.

Don't forget to add compost to the soil regularly to encourage lots of worm activity and guarantee excellent drainage!

But why is this so important?

Under the current climatic (and political) conditions, it is unlikely we will ever live in a time without water restrictions again. By developing water wise gardens and adopting water capture and re-use behaviours such as rainwater and greywater usage, the need to irrigate our gardens with drinking quality water is reduced. While plant choice and groupings, environmental conditions and garden micro-climates are all important aspects of a water sensitive garden, a healthy soil is the most important feature of a sustainable, water wise garden.

Healthy soils with high organic matter content require less water, little to no additional fertiliser and are less likely to change structure and performance during long-term irrigation with greywater. Plants in healthy soils will be more vigorous, robust, and less prone to attack from pests and diseases, saving gardeners time and money. In turn, the environment is spared the damaging affects of prolonged fertiliser and pesticide usage... a great result for us, and future generations.