If the soil in your garden is wet and sticky all winter and dry and rock hard in summer, it's clay!
Clay is the remains of certain types of rocks that have been eroded and weathered to form fine particles. Most soils contain clay particles. A good mixture of sand, silt, clay and organic matter provides the ideal loamy soil. Problems don't usually occur until the clay content exceeds 30-35%. Heavy clay soils are widely distributed around the country.
Many of our Mark Cross and Wadhurst customers garden on very heavy clay. Potentially, clay soils are very good because the clay particles 'hold', but are willing to release plant nutrients to plants. Nutrients are more likely to be washed through sandy or chalky soils by rain.
Clay soils are less prone to becoming too acidic as they hold appreciable quantities of calcium. But these potential advantages are often outweighed by the physical properties brought about by the small particle size.
All soils hold water because it is attracted to particles by surface tension and chemical forces. Clay particles are very small and therefore can hold more water and are less prone to drought. But, as a result they are likely to become waterlogged in winter, making cultivation difficult.
Clay soils are also slower to warm up in spring, (chalk soils certainly don't suffer from this) and so germination of seeds may be delayed. Conversely, they retain heat better than many soils once they have warmed up.
The strong attraction of the water to the surfaces of the clay particles also leads to cracking during dry weather. When plants remove water from clay soils, the volume of the soil decreases and eventually the soil cracks.
During the winter, when rain falls, the soil absorbs water and it swells back to its original volume.
In extreme conditions, waterlogged garden clay soil can have a solid "Iron Pan" within the sub-soil caused by leaching down of iron salts into an impenetrable barrier. This, of course, increases water-logging and therefore gardening problems!
How to live with and how to improve clay garden soil...
a) As we've said, clay soils are fertile and potentially very good. The most important operation in improving clay soil is to try and break it up to reduce the terrible wetness in winter and dryness in summer.
Simple digging will help make a clay soil more workable, but the effect is ten times greater if a bulky organic material is incorporated at the same time. Use peat, garden compost, manure, spent hops, straw or even coarse grit or seaweed: Even very heavy clay soils can be improved as a result.
Beware: You will not improve a heavy clay soil overnight, it may take a number of years before you see visible signs of improvement.
There doesn't seem to be any substitute for hardwork. Any bulky material that is incorporated well into the soil appears to be more effective than just applying to the surface as a mulch.
Clay soil improvers (various proprietary brands are available) and lime will help break up clay soils, but again over a long period.
b) However you improve the top soil, it may still become water logged unless the rainwater can drain through the subsoil. If the subsoil is solid clay, or if you have an Iron Pan or your garden is low lying, some form of drainage may be necessary.
In a large garden, open ditches can be used to collect water and, if possible, carry it to a nearby stream.
In smaller gardens, tile drains, perforated plastic or french drains (trenches of pebbles or shingle) leading to soakaways will help greatly.
c) If you do not have the time, raised beds, above the clay may be a simple and quick solution to many problems.
d) Plant selection, again, is important. It's just not worth fighting your soil. Only plant varieties that you know will tolerate the characteristics of clay soil. A guide to suitable plants can be found here...
e) Be ready to carry out digging, sowing, planting and weeding etc.. in the short periods when the soil is neither too wet nor too dry. Be prepared to cover some areas to be dug with polythene to keep the rain off. Don't walk on wet clay soils. Always work from a plank of wood to spread your weight.