How to get healthy soil

G Magazine

A plant is only as good as the soil you grow it in, and the nutrients of its fruit and veg the same. Read on to soak up some soil-building know-how.


Credit: iStockphoto


Aerobin 400 compost.

Credit: Emma Bowen

soil two two

A hot compost pile.

Credit: Emma Bowen

worm farming

Worm farming.

Credit: Emma Bowen

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On a sunny winter’s Sunday we find ourselves talking rubbish. Well, compost, to be exact. We had joined Adam Kennedy from Milkwood Permaculture for his ‘Feeding your Garden’ workshop and with a slew of other keen green thumbs we were to learn the importance of the very soil we walk on. After all, as said by renowned gardening author Jackie French, “Healthy soil is the stuff that grows things, and keeps on growing those things.”

So what is soil?

Soil is the upper surface of earth that contains a combination of minerals, decaying organic matter, micro-organisms, nutrients, water and air. “Essentially, the composition of an ideal soil is 25 per cent water, 45 per cent minerals, 25 per cent air and 5 per cent organic matter,” says Kennedy. There are a spectrum of soils, with sandy at one end (common in coastal areas, well-aerated and free-draining, with difficulty holding onto nutrients) and clay soils (very fine particles with little air, hard to work and drain poorly) at the other. Loam is in the middle; a good mix of sand, silt and clay.

Why do we need to feed it?

Feeding our soil will help all soils along the spectrum, encouraging stronger and healthier plant growth. Furthermore, when growing fruit and vegetables, we rely on those foods for our vitamins and minerals, but plants can only obtain these if they are in the soil they’re grown in. “When we talk about feeding our gardens we’re actually talking about feeding the soil and the microbiology that exists in the soil, which in turn unlocks nutrients and feeds our plants,” says Kennedy. “In the urban context it’s especially critical because we don’t tend to have very good nutrient cycling. So, we grow food, we eat it and it tends to go down the drain into the oceans; we don’t tend to cycle nutrients very well.”

What do we feed our soil?

The short answer is humus, says Kennedy. “We need to add organic matter, but if we only have organic matter sitting there inert we need soil life to actually turn it into something that is available for plants. So a simple ratio is organic matter + soil life = humus.”

Humus refers to organic matter that has reached a point of stability where it will break down no further. It is that rich dark crumbly black soil. The organic matter that makes it up includes products such as manure, mulch, compost, green manure, food scraps, leaf litter and roots among other organic product. The necessary soil life to break it down includes bacteria, fungi, worms, nematodes, micro-anthropods, protozoa and others. This life plays an incredibly important role in ecosystems. They break down organic matter and minerals into plant available forms, aerate and open up the soil and cycle nutrients. It is believed that there are at least 10,000 species and more than one billion individual bacteria in one gram of soil. “If we can encourage our soils to be alive and healthy, we’ll have aerated soils we won’t necessarily have to turn as much, it’ll be free-draining, available and open to plant growth,” says Kennedy.

We can encourage and introduce soil organisms into our gardens and organic matter using methods including; compost, vermicastings (worm poo), compost tea; brewing some compost as a ‘tea’ to allow microbes to multiply, bokashi bins; using fermenting bins to break down kitchen scraps, and mulching; to break down and add nutrient to the soil. Where space allows, your garden will appreciate a mix of these methods.

Feeding your garden with compost

Compost is basically broken down organic material. Anything that has once lived (including manures, food waste, animal bodies, urine, rock dust, weeds, seaweeds, etc) is compostable. Compost; the final broken down result of these products, is an excellent soil conditioner, improving the soil structure by binding particles together and ultimately improving aeration, water retention and nutrient levels. It also helps to attract earthworms which further these benefits. You may choose to dig the final humus from the compost into the soil, though if your soil is already working ok this can disturb the organisms already in there. So alternatively, spread the compost on top and top with a layer of mulch to protect and keep it moist.

Though there are myriad methods to compost, there are two main composting types: cold (anaerobic) and hot (aerobic).

- Cold composting can be otherwise known as passive composting and is only slightly more involved than piling organic matter together and letting it decompose while keeping it moist. It can be handy for backyards as you build the pile gradually, adding food scraps and plant waste as you get them. The process can take anywhere between 6-18 months to break down, and can be slightly quickened by turning the pile, to add air to it, however otherwise no turning is necessary. A great method if you’re not in a hurry for your compost and don’t want to exert much effort.

- Hot composting is active composting. The difference being that more effort and assistance is required, though you get compost much faster – as quick as three weeks by some methods, or between one to four months by others. Using a cubic metre of the same or similar mix of organic matter, the pile of compost is turned frequently, giving the microbes oxygen and making it more active. The pile becomes hot (up to 65ºC at its peak) due to the activity of the microorganisms, leading to quicker decomposition.

- Though there is a wealth of information available on composting, a great recipe is the A.D.A.M principle:
A - Aliveness: Compost should not be a pile of smelly, rotting rubbish. It is a living system in which bacteria, fungi and other live critters eat their way through your garden waste, turning it into humus. To encourage life, regularly check air, diversity and moisture.
D - Diversity: Diversity in ingredients is the key to a speedy decomposition process. Stick by the golden rule of thumb “if it has lived once, it can live again”, meaning essentially anything organic or natural can be added to your compost (though it is easiest for beginners to avoid things like meat, dairy, dog, cat and human manure and any diseased plants). A good mix of carbon and nitrogen ingredients is ideal. Carbon ingredients are those woodier items that take a little longer to break down such as straw, dry leaves and woodchips, while nitrogen ones break down quickly and easily, such as animal manure and food scraps.
A - Aeration: More air = less smell. Air keeps your compost and it’s live ingredients working. Regular layers of course material, and turning your heap every two weeks can help aeration.
M - Moisture: All organisms in your pile require moisture. Dry material should be watered before each new layer. It should be as damp as a wrung-out sponge.

Feeding your garden with worm farming

The common vertical layered worm farm systems are a great way to not only dispose of your food scraps and organic matter, but to also get great nutrient-rich worm poo for your garden. Starting up a worm farm is easy, with a top tray for feeding the worms, a middle tray for collecting castings and a bottom tray for collecting liquid (worm tea). A good array of organic matter can be added including food waste, tea bags, egg shells, grass clippings among others. Worm castings and worm tea can be harvested on occasion to add to your garden soil. To use the castings, spread over soil. Worm tea should be one part to 10 parts water and used to feed your garden weekly.

You can do this complete hands-on workshop yourself with Milkwood Permaculture. We have just provided a brief overview of their extensive teachings. For more info on their ‘Feeding your Garden’ workshop, or others including natural beekeeping, visit www.milkwoodpermaculture.com.au.