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Improving Clay Soil

You certainly know when you have clay soils, cold and sticky in the winter and baked hard in the summer but the news isn’t all bad. In fact clay soils are very fertile, they just need unlocking and luckily it can be done!

Most soils to varying degrees contain a mix of sand, silt and clay and within clay soils they can present from what is considered a heavy soil with some clay in it, to 100% percent clay. The particles in clay are tightly packed, this means the water and air can’t move freely through the soil.

Usually, unless you have moved on to a new property where the developers have stripped of all the topsoil, you will at least have a layer of topsoil which is workable. But dig deeper to the subsoil and you will find the layer of hard clay and it is in to this subsoil that plants need to push their roots into.

Most of us home gardeners won’t go to the expense of having the composition of the soil tested, as it is its productiveness that we are interested in. It is also usually obvious where on the scale you fit, poor drainage will be your first clue followed by your plant success or failures.

If you are in any doubt then do a simple (non scientific) test yourself, take a handful of soil in your hand and squeeze it, if it stay in a ball and you can form its shape, then it will have a percentage of clay in it.

To unlock all the valuable nutrients and turn it in to productive soils takes a bit of hard work but you will reap the rewards. Clay soils will take a long time to dry out but it is important to let it dry before you begin any work on it. Walking on and working with any wet clay will cause damage, apart from being heavy and difficult, it will compacting the particles even closer together.

  • The first and the hardest part of the job, is to dig over the soil as a rule of thumb you need to at least go down one “spit” depth. A spit is the depth of your spade head; this will bring the clay subsoil to the top, roughly chop any large lumps and then just leave it where it is for at least a season, autumn through to spring is even better. Exposure to the weather will do some of the hard work for you, rain, snow and frost will all help to break it down which is the aim of this exercise.

  • Keep the area clean of weeds, weeds setting seeds in the clay will just be another job that you need to face before you can take the next step.

  • Check your drainage, you will need to provide drains to remove excess water if this is a problem, you can improve the soil but it will still be a wet area if it has to contend with excess water.

The next step is to improve the structure of the soil and this is done by adding all good things to it, you will be able to see and feel the difference as you do this, the soil will become lighter in colour and weight. So keep adding and digging until you see this happening.

  • Clay soil is more often an alkaline soil; the addition of lime is to break down those particles by sticking to them rather than balancing the acidity.

  • Add humus, this is material from the decomposition of any organic matter. It is the humus that adds minerals and soil organisms that all soils need. Blood and bone, compost, leaf mould, green manure are all good sources, animal manures can also be added at this stage, horse in particular is especially valuable – take a drive in the country it is often for sale at the gate.

  • Peat and gypsum is two other ingredients that will help, they are expensive especially over large areas so keep them to treat smaller sections.

Team Tips

  • For a quick and again non-scientific test dig a hole about the size and depth of an ordinary bucket. Fill the hole with water, for reasonable drainage, the water should drain away within an hour or two. If it takes longer then the drainage is not so good.

  • If you want to put in a vegetable garden and don’t fancy all the work, then build up! Vegetable don’t put down their roots as deeply as trees and shrubs so use a raised garden bed to grow your food.

  • If it is just too difficult to treat the soil like a steep bank then borrow from nature for your plant choices and use our own natives, they have adapted well to this kind of soil.

  • Stay away from plants that don’t suit clay by thinking that you can treat a small around the plant. This will just create a bowl for the plant to grow in, that will dry out in the summer and more importantly restrict the roots from pushing out in to the subsoil. It will neither thrive nor cover the bank.


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