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There are an estimated 10 quadrillion (10 million billion) micro-organisms living in a suburban organic backyard, and many tens of thousands of insects and other arthropods, and we'll often find birds, lizards, bats and marsupials. Beneath our feet, in the air, the water and the undergrowth are dramas and wonders, often unseen and unappreciated. Many pest problems are caused by an imbalance – and attempting to destroy the pests can lead to further problems. In permaculture we encourage observation, understanding, and introducing more life rather than removing it wherever possible.
Soil is a living ecosystem. The more biodiverse and biologically active your soil, the healthier are your plants. The healthier your plants, the less disease and the less pest problems you have.
A good gram of organic garden soil has many billions of organisms in it. Plants pump exudates of sugars, other simple carbohydrates, and proteins (AKA 'cakes and cookies') into the soil to feed soil life. Plants need soil life. Microbes create humus and good soil structure, breakdown organic matter and cycle nutrients, provide disease protection to the plants, and form some symbiotic relationships for the access of nutrients.
Bacteria: The most populous creatures in the soil. Bacteria, although single celled have far more chemical tricks than 'more evolved' creatures such as ourselves or plants. They can exchange DNA like trading cards between each other to find solutions to novel chemical challenges very quickly. The glue bacteria create in order to stick themselves to soil particles is important for creating soil structure. Certain bacteria collaborate with legumes to capture atmospheric nitrogen.
Fungi: Underneath the soil lie vast networks of interconnected fungal hyphae (strands). Fungi are especially adept at breaking down woody material and accessing nutrients from rocks. Micorrhizal fungi have a complex chemical language with plants and exchange nutrients for 'cakes and cookies'.
Protozoa: The larger single celled organisms: amoeba, cilliates and flagellates are the main predators of bacteria and fungi, and are vital for nutrient cycling.
Arthropods: Springtails, mites, and insects and their larvae inhabit the soil. They cycle nutrients, create soil structure with their fecal pellets, and are 'taxi cabs' of the soil, moving bacteria and fungal spores around.
Earthworms: According to some calculations, earthworms collectively provide the earth turning capacity of five horses per acre in earthworm rich soil. However they do this in a way which improves soil structure, not destroys it. They aerate the soil with their burrows, breakdown organic matter and introduce excellent soil biology in their castings.
Nematodes: These microscopic worms are also bacteria and fungi predators. Some types also attack plants such as tomatoes, however rich and diverse soil biology mitigates this.
Like you, your soil needs air, water, shelter and a balanced diet.
Compost and mulch: Well made compost is a hothouse of healthy soil life. Compost introduces both the life and humus needed to maintain that life in the soil. Humus creates good soil structure which allows air and water to penetrate, provides habitat for soil microbes, and is a medium for nutrients to be stored. See the VeryEdibleGardens.com iVEG page on compost, or come to one of our Compost and Worms courses to learn how to achieve a balanced diet and make a good compost. Harsh winds dry the soil while direct sun kills exposed microbial life. Mulch provides both shelter for the soil, temperature control, and food for the microbes who eventually turn that too into humus.
Aerobic vs anaerobic life: The type of organisms congenial to good plant growth are aerobic – ie. those that live in oxygen rich environments. Good aerobic compost actually kills human and many plant pathogens. Make sure your compost is well aerated using strategies such as drilling holes in your compost bin, adding at least as much carbonous material such as straw or cardboard as food scraps to your pile, turning the pile with a fork or compost screw. Don't use too much water on either your soil or compost – they should be moist, not soaking – and don't walk on, or regularly dig your garden soil, to maintain good structure so air can get in, and water can drain.
Fungi to bacteria ratios: Trees and other perennials prefer fungi dominated soils, whereas vegies prefer bacteria dominated soils. Increase the woodiness of your mulch or carbon level of your compost to encourage more fungi, and lower it to encourage more bacteria. So use wood mulch for trees, straw for vegies.
Common garden insects:
Aphids: A common garden pest across many species of plants. Aphids can reproduce asexually and build populations rapidly. Are sometimes 'farmed' and protected by ants, who eat their sugary secretions. Predators include parasitic wasps, hoverfly larvae, lacewing larvae, ladybirds and spiders. Can be hosed off with a strong get of water. As a last resort can be controlled by garlic spray, white oil, pyrethrum spray and others.
Whitefly: Can be a serious sap sucking garden pests. You'll see clouds of tiny white moth like insects when they are disturbed. They can cause a yellow mottling of the leaf, spread diseases, and invite fungal attack. Most aphid predators are also whitefly predators. Some people vacuum them off with a portable vacuum on cold morning when they are slow. Sprays which work on aphids generally work on the closely related whitefly.
Scale: Although it doesn't look like it, scale is also an insect, one related to whitefly and aphids, which however loses functionality of its legs in adulthood and forms a shell. A problem of citrus trees and some other trees, not vegetables. Whiteoil can control it, if it seems to be out of control.
Cabbage white butterfly: Attracted to everything in the cabbage family, it's important to control the caterpillars, especially when plants are young. Natural predators include small birds and parasitic wasps. Physically pick off the caterpillars, and rub off the tiny eggs. BT sold as Dipel and other products is a bacteria based spray which attacks only caterpillars.
Ladybirds: One of the gardener's best friends, the ladybird and it's larvae (pictured) are voracious hunters of aphics, whitefly, small caterpillars and other garden pests. They aren't active in cold weather, but where aphids are found they are usually quick to follow, especially if you provide the right flowers to attract them (see below).
Parasitic wasps: These tiny wasps are ubiquitous, but so small that you have to look for them. Different species are adapted to different garden pests, including aphids, whitefly, caterpillars. Some even attack other parasitic wasps! They like the same kind of flowers as ladybirds (see below). Look out for the hard brown shelled aphids – they have been infected by the wasp larvae. They are tiny and harmless to humans.
Hoverflies: These small flies with bee like markings eat mostly pollen, however their larval offspring love to chew through aphids and other small pests. They like the same kind of flowers as parasitic wasps and ladybirds. This one is on a calendula.
Praying mantises: Incredibly strong predators, they eat anything and everything (including other predators). They are elegant and lovely to watch, and good guys in the garden.
Common garden macro-fauna
Spiders: No insect predators do more work than spiders. Some are free ranging hunters, some make webs. Few are dangerous to humans, so try to learn to love them.
Snails and slugs: If young seedlings are going missing overnight, or large holes appearing like those pictured, the culprit is likely slugs and snails. They generally only come out at night. You may find their slime trails. Some birds, frogs, lizards and rodents are predators. Chickens love them, and having a chicken run near the veggie bed seems to offer some control. Beer or sugar water placed in a bowl and buried to soil level is an effective trap. Start putting them out a few nights before planting to clear populations first. Coffee grounds can provide a physical barrier.
Centipedes, millipedes and slaters: These many legged arthropods perform different roles in the garden. Centipedes (pictured) are predators. Millipedes and slaters generally eat decaying organic matter. Slaters sometimes eat seedlings but are generally not a problem.
General garden strategies:
Start with the soil, as healthy soil allows plants to have strong immune systems.
To attract predator insects such as ladybirds, hoverflies and parasitic wasps, the following types of flowers are useful:
- Umbelliferous plant flowers. This includes carrot, dill, fennel, parsley and others
- Daisy family
- Marigold family including calendula
- Providing water for predators in the form of a small pond is useful. Put rocks around to provide habitat for frogs and lizards.
- Provide habitat for small birds with dense native plants. Grevilias, fuscias and banksias bring in honey eaters and wattlebirds which also eat insects.
As a last resort, you can make your own organic sprays using ingredients such as potassium soap (available from nurseries) or oil and water to smother and suffocate insects. Herbal infusions of garlic, chilli, wormwood, tomato leaf and many others help with various pests.
Our favourite organic pest control book is the 2010 release Bug by Tim Marshall (see below). Here's Tim's quick garlic spray recipe:
Garlic spray recipe
To make a large quantity of garlic spray, follow this recipe:
500g crushed garlic 150-200mls liquid paraffin (just enough to cover garlic) 2.5L water 150g pure soap
- Soak the garlic and paraffin together for 24-48 hours
- Add remaining ingredients and stir thoroughly
- Filter the mixture well (a commercial filter or sieve is best, but a piece of muslin or tea towel will suffice).
- Store in a glass container (flagon bottles or jars are excellent), away from sunlight.
- Dilute at the rate of 15-30mls of concentrate per 1L of water, depending on use
Resources iVEG: Our growing source of organic gardening fact sheets. www.veryediblegardens.com/iveg
Green Harvest: Organic gardening supplies and a great information source on common garden pests: www.greenharvest.com.auSoil Foodweb Institute: For analysis and information about soil biology: www.soilfoodweb.com.au
- Organic Gardening by Peter Bennett includes an excellent introduction to the common life in your garden. Available through www.veryediblegardens.com
- Bug: The Ultimate Gardener's Guide to Organic Pest Control by Tim Marshall – absolutely great Aussie organic pest control book, recommended by Peter Cundall
- Insects and Gardens: In Pursuit of a Garden Ecology by Eric Grissell is US based but a fun and involving read about backyard ecosystems with a focus on insects.
- Teaming with Microbes by Jeff Lowenfels and Wayne Lewis is a gardeners' introduction to the life of the soil.