You may have to set up garden beds on a lawn area. If the lawn contains couch or kikuyu, digging out the grass will not be sufficient as these two grasses will regenerate from small pieces of runner left in the soil. See EOG&MP pp 440-1 for a guide to turning couch and kikuyu grass areas into garden beds.
On the other hand, you may have to set up garden beds on unimproved soil, or where topsoil has been removed during building construction. Organic gardeners practice minimum cultivation because regular cultivation damages soil structure and accelerates the loss of carbon from soil. However, some initial cultivation may be necessary to break up very compacted ground.
Before you cultivate, it will help if you can identify the texture of the soil in your school grounds. To do this you will need a sample of soil from your garden bed area.
Take a handful of dry soil. If soil in the garden bed area looks hard, try scratching it with the point of a trowel. It may be sandy with a surface crust, but if you need a shovel or trowel to collect your sample – you do not have sandy soil.
Set the sample aside and apply some water to the garden bed area. Take note of how the water behaves. Does it soak in, or bead and run off? Does the soil have a crust when dry, and drain poorly when wet?
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.
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