When I mentioned at work I was moving to Brinkworth, I remember a colleague saying that he’d never move to an area with clay soil. At the time I was not such a keen gardener, but of late I can see where he was coming from. I am always envious watching gardening programmes when they dig into the soil and this lovely friable crumbly stuff falls off their fork. No stabbing a large lump of clay and then bashing it for five minutes for them!
Brinkworth and much of the surrounding area is underlain by Oxford Clay, about 50-60m depth under my house. Oxford Clay has many beneficial qualities, good for brickmaking, dinosaur fossils and landfills! Not so good for gardening and drainage.
The soil itself if not so bad if left relatively undisturbed, but tends to be prone to waterlogging in winter and drying out in summer. And as for digging, well, it’s hard work.
In my garden the natural topsoil is about 30cm/1 foot depth, or in gardening terms a spade’s depth. Just to make things more fun there is a stony layer on top of the clay, meaning every time I dig, large stones are introduced into the topsoil.
There are some easy fixes, the most obvious being raised beds. I have a few and they are great but the main drawback is the shear cost of buying soil. More than a few and you’re looking at hundreds of pounds just to buy in soil. Of late the “no dig” method is fashionable and is much promoted in the media. This consists of adding a large layer of mulch each year, which suppresses weeds and improves the soil. It does work to an extent on clay soils. It works best for raised beds, and areas were you don’t have perennial weeds such as bindweed. In my garden due to a combination of bindweed and clay soil it works for 1-2 years and then you need to dig over to uncompact the soil and remove the weeds.
So, what do you do if you want to grow directly in a clay soil? Timing: Knowing when to work the soil is very important. Working it when it is too wet does more damage than good, is very hard work, and is generally not fun. Too dry and a clay soil is rock hard and require a lot of effort just to get the spade in. The ideal time to dig over is late autumn, but if the weather is not on your side be prepared to leave it until spring. The last few years I have not dug the plot at all due to an autumn deluge, relying on my cultivator to lightly scratch the soil in spring before planting. This year, the dryish autumn has been kind and most of my plot has had the benefit of a good dig over and weed removal.
Digging: Sensible people use a small bladed spade and take very thin slices, which means the soil breaks up easier than if you take large slices. Being not sensible, I take massive chunks and then spend ages bashing it with the spade to make it breakdown. In my defense I use a long handled spade, which gives better leverage, but don’t do as I do etc. Post digging back ache is a reoccurring theme. In my garden due to the stone layer I do not double dig (digging down two spade depths) and I try not to bring the stones up. Even so, I usually spend quite a while picking out the pesky stones. My approach is to dig over, add manure and leave to overwinter, and then use a cultivator to break down the large clods in the spring.
Organic matter: It doesn’t really matter what but incorporate lots of organic matter, so garden compost, manure, grass clippings etc, mulch on top of the soil and dig in. Don’t underestimate simply adding grass clippings to the soil. I use them as a weed suppressant in summer and let them rot in overwinter.
Adding lime: Adding lime raises the pH of acid clay soils, making them more alkaline and in doing so it encourages the clay particles to stick together in small(er) clumps. This makes the soil more friable and easier to work. The best time to apply is after digging, and allowing to work overwinter.
Cultivators: I use a Mantis cultivator. It’s not powerful enough to deal with clay soil without initial human help though. Due to bindweed, I still need to hand-dig, so deep rotavating is not really an option. However, once dug, mulched and left overwinter the Mantis is ideal for breaking down the soil into a workable medium.
Watering: Waterlogging in winter and drying out in summer will be a problem, be prepared to lose plants in winter (strawberries and herbs like sage and rosemary really do not like being submerged) and water lots in summer.
So if you have a small garden, consider raised beds. If you have a large allotment plot, add lots of mulch and dig over every 2-3 years. And be prepared to leave the soil alone if the weather is not on your side and water lots in summer.
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