Feed the soil, not the plants, we've been told. If you feed the soil, the plants growing in it will take care of themselves.
But it's not quite so simple, according to Cherryle Prew, of Soil Foodweb International NZ, the Roxburgh-based branch of an international soil biology group.
Because it's not the soil that needs feeding, it's the billions of life forms that live in it.
Keep them happy and you keep your garden - vegetables, flowers, fruit and trees, even lawns - happy too.
According to the United States Department of Agriculture, a single spadeful of rich garden soil contains more species of organisms than the entire Amazon rainforest.
These tiny gardeners, which spend their days aerating and fertilising the soil as well as helping plants take up nutrients to make them stronger, make up the soil food web.
This web is a complex interaction between all the organisms in the environment.
At its base come the plants and other organic matter from animals and microbes.
These become food for fungi and bacteria, which in their turn feed protozoa, nematodes, worms and arthropods, including insects.
Now we get to the part most gardeners are familiar with: the birds, which are the top level of the soil food web in New Zealand.
All these life-forms work together to create the perfect environment for a garden, and if they get out of balance too badly, the plants will begin to suffer.
Compost is one key to a happy soil food web, Cherryle says.
It doesn't much matter if it is made at home or bought in, though she recommends taking extreme caution with compost purchased in bags.
Read the label, open the bag outside and wear gloves and a mask when you handle it.
Don't breathe the dust in case it contains fungi or disease-causing bacteria.
If making your own compost, she suggests researching composting methods at the library to ensure the best results.
Chlorinated tap water doesn't hurt the soil life as long as it is not overused, Cherryle says.
Soil containing plenty of organic matter will require less watering anyway.
And there's nothing wrong with the occasional bit of chemical assistance in a plant-health crisis, she says.
But she recommends using compost, seaweed and fish to help correct soil imbalances and foster healthy growth, rather than automatically reaching for the superphosphate to give a quick but short-term boost.
Growing our own food makes sense to many of us these days.
Freshly harvested food tastes better and can contain more vitamins.
But if food grows in degraded soil, its nutritional value will also be degraded.
A healthier soil biology can help give us a healthier diet. Not to mention a beautiful flower bed.
Soil health terms
The Soil Foodweb reference guide glossary of soil health terms
Fungi
Comprised of microscopic cells that grow in long threads called hyphae, which bind soil particles, increasing the soil's ability to absorb and retain water.
Fungi play an important role in breaking down organic matter into useful forms and assist in nutrient retention and disease suppression.
Bacteria
Help break down organic matter, maintaining the soil's ability to retain nutrients, assisting in disease suppression and helping improve soil structure.
Certain types of bacteria break down toxic compounds and assist with nitrogen fixation. Protozoa Single-cell organisms that mainly consume bacteria and release nutrients in forms that can be absorbed readily by plants.
There are three different groups of protozoa in soil - flagellates, amoebae and ciliates.
Nematodes
Classified based on their food source - fungal, bacterial or root feeders. There are also predatory nematodes that eat other nematodes.
Most nematodes are beneficial as they form an integral part of the soil food web. They convert nutrients into forms available to plants by consuming either fungi or bacteria.
Beneficial nematodes consume disease-causing organisms and are an important food source for larger organisms.
Mycorrhizal fungi
Colonise the roots of most plant species, forming a mutually beneficial relationship that has a significant role in nutrient uptake and protects against root-feeding nematodes and pathogens.
Mycorrhizal fungi are important in that they supply plants with phosphorus.
Source: Soil Food Web International NZ www.soilfoodweb.co.nz
What have I got?
- Soil pH testing kits are available for about $20 from garden centres.
- Electronic soil pH testers are also available, from about $37.
- Soil testing kits with instructions and courier bags are available from rural supply stores.
- Samples are taken according to the instructions, then couriered to NZ Labs at the Ruakura Research Centre, who will provide a soil profile for about $75.
- Soil Foodweb International (NZ), in Roxburgh, provide a range of soil testing services. Forms, prices and instructions are available from their website.
