Testing the soil texture
Remove any stones from the sample and, using a spray bottle, add just enough water to allow you to knead the soil in your hand. Does it feel, gritty, silky, smooth or sticky?
Roll the soil into a ball. Watch how the soil behaves. Then, roll the ball between your palms to make a log shape. Try to bend the soil log into a curve.
If you were unable to form your soil into a ball, it is very sandy. If the ball broke apart, you have a sandy loam. These soils, and soils that form a crust, need a lot of organic matter in the form of compost added to them for the healthy growth of plants. Adding some bentonite (a volcanic clay) can also help these soils retain moisture.
Did your soil feel only slightly gritty and form a ball and a log, but broke when you tried to curve the log? You have an easily crumbled (friable) loam that probably contains some organic matter. This soil type is good for garden beds, and requires little cultivation. Your soil will benefit from a 3-5 cm layer of compost dug into the top 10 cm of the garden bed, regularly.
If your soil was hard to collect, felt quite smooth, and the soil log cracked but did not break when curved, you have a clay loam. Clay soils retain more nutrients than sandy soils but clay particles are very fine, which restricts water, root and air movement through soil because clay particles sit together like a stack of wet dinner plates. The addition of plenty of compost to topsoil or growing a green manure grain will help improve these soils.
If your soil ball was like hard plasticine, and the log did not crack when bent, you have a clay soil. Clay soils tend to crack when dry and stay sticky when wet. Sticky soils may respond to applications of natural gypsum, preferably organic-allowed gypsum. See EOG&MP, pp 37-8 and pp 442-3 to test your soil's suitability for gypsum application.
If soil in your garden area is in very poor condition, it might be worthwhile to purchase enough compost or organic topsoil to set up one bed to allow students to get started on their gardening, and grow a green manure grain in the rest of the gardening area. Use the slashed green manure as mulch to protect the soil surface. Roots of annual grains break down to provide a lot of organic matter.
Oats, barley and wheat are a good choice as they are fast growing and provide a lot of organic matter. Oats and wheat are also cheap, and usually easy to find. For an easy to follow guide on growing green manures, and a table of which green manure to grow when for each climate, see EOG&MP, pp 14-18.
If your soil forms a crust when dry, feels silky, and the log breaks quickly, you are likely to have a silty soil. These soils can contain nutrients but their very fine particles pack down, excluding air. Silty soils will benefit from green manures that add bulk (e.g. oats). When turned-in they aerate these soils and help them form aggregates. Silty soils are not common, but some soil suppliers combine dredged soil with sand, which produces a poor medium for growing plants. Check the quality of topsoil before purchase.
- Return to top of page
As stated in Part 1 of the Introduction, organic gardening and farming focus on maintaining soil health. If soil is healthy, plants are healthy. See EOG&MP pp 5–8, for a detailed explanation on the importance of healthy soil in successful gardening.
Compost is the foundation of garden soil health. Good compost contains all the minerals that plants, animals and humans need for good health, most of the soil's nitrogen, and humus. It provides a habitat for a soil community of millions of beneficial bacteria and fungi and other organisms that help form soil aggregates, increase the depth of topsoil, control soil-borne diseases, and feed nutrients to plant roots through a symbiotic relationship.
Humus, the most stable form of recycled organic waste, stores carbon in soil, keeps soil more moisture-retentive yet better-drained, and buffers plant roots from temperature extremes and unsuitable acidity or alkalinity of surrounding soil.
Basically, there are two methods of composting – aerobic (with oxygen) and anaerobic (without oxygen). See EOG&MP p 33 – Organic Fertilisers for further information.
Well-made compost provides perfect conditions for the healthy growth of fruits and vegetables. The vegetable patch and orchard require the most compost because nutrients are continually being removed as crops are harvested. Consequently, we recommend aerobic or 'hot' composting (Indore method) for school gardens, as it is the fastest method of providing a steady supply of compost. With this method compost can be ready to use in 6–8 weeks in most parts of Australia.