A loosen soil rich in humus and nutrients, with a slightly acidic to neutral pH value, is optimal for most garden plants. You will rarely encounter such ideal conditions but, fortunately, you have centuries of garden wisdom to call on to help improve the soil in your beds.
Most soils are a combination of sand, clay and silt, and the proportion of each determines the type of soil you have. You might have anything from light sandy soil, which contains mostly sand, right through to heavy clay – a soil that is predominantly clay – and any combination in between. The ideal is a loamy soil, which has roughly equal parts of sand, silt and clay, plus plenty of added organic matter and a crumbly texture.
Soil Types
- Sandy soil is loose and easy to work so plant roots can spread out easily in it, but water and nutrients are poorly absorbed. Use compost to increase the amount of humus and mulch to prevent rapid drying.
- Clay soil makes it difficult for roots to spread. The soil can be so tightly compacted that the roots of many plants can’t penetrate it to reach water and nutrients, so the plants will wilt quickly. Loosen clay soil by adding large amounts of organic matter. Clay soil is nutrient-rich and holds water well.
- Loamy soil offers the best gardening conditions. It stores water and nutrient effectively and the soil structure is loose enough for plants to root easily and reach the nutrients. By adding a little compost or organic fertiliser each year, you can ensure that the soil doesn’t become depleted over time.
Soil Analysis
Determine soil types before you start gardening to ensure you choose the right one for your plants.
- Take a spade sample at several places in your garden, digging to a depth of about 30cm.
- Sandy soil will feel gritty when you rub it. Dampen a handful of soil. If you try to form a ribbon of soil by pushing it between your fingers, you’ll be able to form only a centimetre or two.
- Clay soil will feel smooth and may stain your fingers. You may be able to form a ribbon of soil several centimetres long.
- Loamy soils are crumbly and there could be lots of plant material in it due to the high organic matter.
- Alternatively, determine soil conditions by examining the roots of plants currently growing in your garden, a small root ball and crooked, intertwined root strands point to impenetrable soil.
- Look for creepy-crawlies. The presence of many helpers such as woodlice, earthworms and millipedes in the soil is a sign of good soil quality.
Acid and Lime Content
The health of garden plants may well depend on the soil’s acid content. Some plants grow well in acidic or alkaline soils, while others don’t. Look into neighbour’s gardens to see what plants thrive there.
- Alkaline soils are indicated by the presence of yarrow. These include Solomon’s seal, bergenias and hellebores.
- Acidic soils: camellias, azaleas, and blueberries
- A high lime content is indicated by the presence of bellflowers, marigolds, delphiniums, cornflowers, lavender, alliums and spurge.
- Spray a little vinegar onto a clump of soil. The vinegar will bubble when it comes into contact with soil containing lime.
Soil Improvement
The type of soil you have doesn’t determine whether your plants will grow well. Although generally fertile, clay soil can be compacted, while sandy soil (even though well-drained) can be lacking in nutrients – both of which affect plant growth. Adding the right substances improves most soils.
- Add compost or manure to sandy soil regularly to improve the structure and increase the amount of water the soil can hold.
- Dig garden lime or dolomite into highly acidic soil in autumn, add phosphate and potash in the form of wood ash.
- Break up heavy clay soils by adding compost or manure regularly – ideally in spring and autumn.
- Use organic mulches such as lucerne, sugar cane, coco peat or bark, as they break down over time and add extra organic matter to the soil.
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