Squeeze a handful: clay is heavy and sticky and cracks open in drought, sandy soil is light, raspy and refuses to clump, and between them sits loam, fertile and good at holding water. Read colour, texture and the weeds that appear, and you will know what to add and which plants will thrive.
The major constituents of soil are clay, silt, sand and humus. The relative proportion of each constituent determines the type of soil. It can be clay, loam (for silt) or sandy. Its texture, pH, and water retention or heat retention properties depend on how these elements add up.
To know it in detail, it is possible to send a sample of your soil to a laboratory for analysis. Kits sold in in horticulture stores can let you estimate pH and how fertile the soil is quite easily, too. But most often, it is simply enough to knowingly observe the color, texture, and spontaneous growth (weeds) that grow there.
The relative proportion of clay, silt, sand and humus decides which soil you have, and each one behaves differently in the hand, in the rain and in the heat. Use this table to place your own garden before reading the detail below.
| Soil type | Feel in the hand | Water and warmth | Indicator plants | How to improve |
|---|---|---|---|---|
| Clay | Heavy and sticky, dense and compact; a squeezed handful flattens into a circle without splitting | Holds water, cracks open in drought, slow to warm, favours late crops | Field milk thistle, smartweed, thistles; pH neutral to acidic | Add compost and fertiliser; spade it over in late autumn |
| Loam (silt-rich) | Average, intermediate texture; a flattened handful splits before 1/5 inch (5 mm) thick | Retains water well, but seals into a surface crust after heavy rain | Very fertile good-quality soil; texture, not acidity, so test the pH | Sow green manure in late autumn; break any crust with a rake or mulch lightly |
| Sandy | Light and raspy; a handful does not clump together at all | Poor water retention, heats up fast, gives early crops | Anthemis and pansies; poor soil, sometimes acidic | Compost and fertiliser regularly, in small repeated doses; keep the surface mulched |
| Chalky | Fizzes when white vinegar is poured on it; the more bubbles, the more chalk | Basic pH | Many plants adapt to chalky or limestone soil | Add manure and till green manure into the soil |
Whatever the type, avoid walking on the bed while the soil is wet, since damp soil compacts underfoot.
Easy to recognize, this is a heavy, sticky soil that cracks open in times of drought. Dense and compact when you pick a handful of it up, you can flatten it to form a circle without having it split. The flatter you can get the circle to be before it splits, the higher the clay content!
Field milk thistle, smartweed and thistles are among the plants that spontaneously thrive in this type of soil. The pH of the soil is generally neutral to acidic. To amend it, you would usually add compost and fertilizer. Spade it over before winter.
This is an intermediate type of soil, with an average texture, and it retains water well. Very fertile, it is neutral in terms of acidity. If you gather up a handful and flatten it out, it will split before you reach a thickness of 1/5 inch (5 mm).
This is good quality soil, and you can enrich it further still if you sow green manure before winter.
After heavy rain, silt-rich loam often seals into a thin surface crust that can trap emerging seedlings, so break it gently with a rake or head it off with a light mulch.
Avoid walking on the bed while the soil is wet, since any damp soil is vulnerable to compaction underfoot, especially loams with a high silt or clay fraction.
Loam describes soil texture, not acidity, so loamy soils may be acidic, neutral or alkaline; test the pH before liming, since unnecessary liming can raise it too high for acid-loving plants.
Light, raspy soil doesn’t retain water very well and heats up fast. It doesn’t clump together when you pick a handful up. Sandy soil will help produce early crops, whereas clay soil tends to be more favorable to late crops.
Anthemis and pansies naturally grow in sandy soil. This is poor soil, and it is sometimes acidic. Adding compost and fertilizer on a regular basis will help enhance it.
Nitrogen and potassium leach quickly through sand, so give fertiliser in small repeated doses rather than one heavy feed.
Keep the surface mulched with straw or grass clippings: it slows evaporation and the material feeds humus into the soil as it rots down.
To know if your soil is chalky, simply pour some white vinegar on it: the more it bubbles, the more chalk is in the soil (basic pH).
Many plants can adapt to chalky or limestone soil. Adding manure and tilling green manure into the soil will help make it better.
Laure Hamann
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Test a crumb dug from planting depth as well as the surface, since an imported or composted topsoil can fizz quite differently from the chalk beneath it.
