Understanding your soil is starting point for gardeners

Gardening on the Edge by Diana Wayland

The ‘virgin’ clay soil on the right – note the piece to the left of the sample with the thumbprints in it. To the left is soil that has been improved by previous occupants – its texture is much more open and friable. In the center is a pH meter, showing that the soil is neutral at pH 7.

Soil is the foundation of a garden. Often overlooked, it is the key to growing success.

There are five main types of soil – clay, sand, silt, chalk and peat. Knowing which one yours is will indicate what you can grow in it.

In Caithness it is unlikely to be chalk. Where we live the virgin soil is a heavy clay. Not far from us, however, the soil is peat. Both may contain elements of silt or sand, but ours only does where it has been improved by past gardening, and that is only in a few areas around the house.

Clay soil is heavy, sticky when moist and hard as concrete when dry. Adjacent fields contain rushes, indicative of poor drainage, and local farmers have installed field drains to improve some of them. It is neutral, pH 7. Ours is more alkaline where it has been improved.

Peat soil is dark and of a spongy consistency, containing much decomposed organic matter. It can, however, become waterlogged and require drainage. It is also usually acidic. This means that only a few select plants, like rhododendrons or camellias, can access the nutrients in it – easily rectified by adding lime.

The pH of your soil is quite important. Ours is a bit too alkaline for tatties and they get scab unless I reduce it from the usual 7 down as near as I can get to the ideal 5.5. It is easy to check the pH of your soil. There are many pH test kits available, from ones where you mix the sample with water, add a chemical then check the color against a chart, to a much easier one that only requires you to stick its pointed end in the ground.

In extreme cases drains will be needed to improve waterlogging in either soil. Our clay soil dries out in drought so its main need is something to increase the gaps between the tiny particles that make it up. Sand can clog it further, but grit can help. However, grit is heavy, bulky and expensive.

In small gardens raised beds or containers are helpful. You have control of the soil with these.

The best way to improve a heavy clay soil is by the addition of organic matter. And, oddly enough, the same goes for light sandy soils. Both improve the soil texture and enable soil organisms to start producing humus which is vital for the health of any plants. Humus is dark organic matter produced by the decomposition of plant and animal matter. It is rich in nutrients which plants then use to grow.

There are numerous sources of organic matter. One is well-rotted manure. This is fine if you also want to develop a rich soil, but it can be too rich for some plants. Seaweed is also extremely good, for those living on the coast, but needs careful handling. Gather it before it dries out and lay it thinly on the soil. It is best if composted. You can use spent potting compost.

Leaf mold, left to rot for two years after gathering, is excellent. But that is a problem in some parts of Caithness. No trees.

However, you can easily make your own source of organic matter, from materials you will already have to hand. Garden compost. I will be showing you how to do that next time.

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