Heavy Soil

Clay soils are often described as ‘heavy’ soils due to the sticky texture when digging and they are often liable to waterlogging. Consequently, the drainage and aeration are poor, taking a long time to warm up in spring, whilst drought conditions will cause the soil to form hard clods and crack into wide fissures, making it difficult to maintain.

However, a clay soil is highly fertile as it retains moisture and the nutrients required for plant growth due to a slight negative charge.


Improvements are chiefly carried out by deep digging, but timing is important as the clods formed when digging wet clay will dry out into hard lumps unless exposed to a winter frost. Late autumn or early winter are ideal for single or double digging. When double digging fork over the sub-soil and leave the top spit rough and unbroken, allowing largest area exposed to the weather action.

Lime can be added to the top 6 inches (150mm), causing a reaction called flocculation, which helps to break the soil down into a crumbly texture.

If liable to waterlogging, drainage can be improved by added Cornish grit or coarse horticultural sand to sub-soil when forking over.

High water tables can be lowered by creating open ditches allowing water to run away, but in extreme cases drainage pipes may be necessary.

The addition of well rotted manure, garden compost and lime (Clay soils are often acidic) will help lighten and make it more of a crumbly texture.

Avoid walking in the soil when wet, causing compaction and try to keep the soil surface covered with plants or mulching.

Vegetable growing can be aided by the use of small raised beds – 4ft x 4ft (1.2m x 1.2m) or 4/5ft (1.2/1.5m) wide and as long as you like – even where a high water table exists. Thus ensuring that the soil is not walked on but cropping is within arm’s reach.

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