Healthy soil is the foundation of every successful garden and no matter how poor its condition or whatever type it is, all soils can be improved by regularly adding organic matter. Compost, manures, lawn clippings, kitchen scraps, vacuum cleaner waste, weeds, prunings, paper, wood shavings and mulches are all sources of organic matter. Healthy soils contain thousands of minute, soil-borne life forms called micro-organisms. Many of these life forms don’t even have scientific names but the wonderful thing about them is most are harmless and many are beneficial, actively suppressing soil-borne diseases.

Sweet or sour

So how do you get these benefits working in your garden? First, find out whether your soil is acidic (sour) or alkaline (sweet). Highly acidic or alkaline soils lock away nutrients already present, limiting access to them by plants. Just adding extra fertiliser won’t improve things. A soil pH test kit, available for about $20 from garden centres and hardware stores, reveals all in minutes.

The gardener’s ‘Holy Grail’ is soil that’s neutral – neither alkaline nor acidic – a condition where most nutrients become available to most plants. Alkaline soils can also be neutralised by adding either chelated iron, powdered sulfur or iron sulfate, while acidic soils can be neutralised by adding lime or dolomite. These soil conditioners, all available at garden centres, gradually improve soils. Once a neutral result is achieved, maintain it. Test your soil before adding any conditioners then retest every six months to check its progress.

Special problems

If you live in a new home there’s a chance your topsoil has been added after the building work. Therefore, it may be very different from the natural soil in your district and need different conditioning.

If you have an old garden and the soil has been regularly fertilised, it may be good for common flowers and vegetables, but it could have too much phosphorous to successfully grow phosphorous-sensitive plants like grevilleas, banksias and proteas.You can find out all about your soil by sending samples for analysis in a soil laboratory. The upfront cost is about $350– $450 but the knowledge you gain eliminates guesswork, and in the long term saves you money on non-essential fertilisers and soil conditioners.

Seaweed benefits

Most Australian soils are naturally low in boron, magnesium, potassium, zinc and selenium. This won’t affect most native plants, but limits success with some exotic ones. The easiest way to supplement these and to stimulate healthy soil simultaneously is to use commercially available seaweed fertiliser regularly. Seaweed fortified with fish is useful because fish adds calcium, which helps plants to absorb phosphorous more effectively.

Keep the benefits of added nutrients and conditioners, such as seaweed, by composting all healthy garden prunings and refuse to recycle added nutrients and conditioners.

Cultivate good guys

Mulching your soil feeds beneficial soil micro-organisms, the ‘good guys’ that help suppress diseases. Soft, leafy, nitrogen-rich materials, like lawn clippings, vegetable scraps, sugarcane, lucerne and straw mostly benefit bacteria. Hard, woody, carbon-rich materials, like bark, tea tree and woodchip mostly benefit fungi.

By varying the types of mulch you use each time, you stimulate different types of soil micro-organisms. That’s why compost made from a balanced range of materials is so beneficial. Neutral soil that’s regularly improved with a diversity of mulches is another key to healthy, robust plants.

We haven’t mentioned feeding plants at all. That’s because if you work at developing well-composted, well-mulched, neutral soil, eliminate nutrient deficiencies and feed your soil with seaweed products it sustains, protects and nourishes all manner of plants. And this is the secret of good gardening – the best results come from feeding the soil, not your plants.

How to achieve tip-top soil

  • Find out if your soil is acidic or alkaline by testing it with a soil pH test kit, available at all good nurseries.
  • Gradually condition the soil to achieve a neutral test result, repeating tests every six months.
  • Keep soil loosened by digging and regularly supplement organic content by adding compost.
  • Use a variety of mulches to stimulate both bacteria and fungi.
  • Starve soil-borne diseases by removing any dead tree, palm or shrub stumps.
  • Stimulate beneficial soil life by regularly using seaweed fertiliser.
  • In new or difficult sites, have soil tested at a laboratory.

Keep it clean

Some types of garden refuse aren’t worth recycling, like tree stumps and shrubs that have died from soil-borne diseases. Infected stumps can remain potent sources of infection for nearby plants for many years. Remove as much infected material as you can – don’t recycle it – to help starve diseases.