Herne Bay Allotments and Gardens Association












Clay soils are:

Heavy to dig and cultivate

 Drain slowly after rain

 Warm up slowly as summer approaches, leading to delayed plant growth and ‘workability’

 However, against this, they hold water well

 Are usually rich in plant nutrients

Warning: if worked or walked on when wet they lose their structure, and become puddled and compacted. Remedying this is slow and laborious; so  damage should be avoided at all costs.

Techniques and tips if you garden on clay soil:

 Dig in autumn and early winter when relatively dry. Once wetted by winter rains, clay soils often cannot be worked or walked on until mid-spring

Allow winter frosts to work on clay and break it down

Where digging is required, it is traditional in wet regions to dig clay into narrow ridges to allow more frost activity and better drainage

There is often only a brief period when clay soils are workable between waterlogged soils after winter and baked hard clay from late spring

Avoid early planting or sowing unless drainage can be improved by making raised beds or the ground dried and warmed in advance (for at least six weeks) by covering with cloches or clear polythene sheets

Five steps to improving clay soils:

 1. Make  to assist drainage and to reduce trampling of the soil

2. Consider adopting a ‘no-dig’ regime, especially in raised beds, as these suit clay soils well

3. Some, but not all, clay soils respond to extra calcium, which causes the soil particles to flocculate (clump together). Where the soil is acid, Lime can be applied, but elsewhere it is better to add gypsum. Gypsum is the active ingredient of many commercial ‘clay improvers’. Test on a small area in the first instance to ensure it is effective on your type of clay

4. Dig in plenty of bulky organic matter such as manure or, ideally, composted bark, as this can make a noticeable improvement to the working properties of clay

 5. Apply organic around trees, shrubs and other permanent plants as these will reduce summer cracking and help conserve moisture

Adding grit, sand or gravel to clay soils:

Clay particles are amazingly dominant in a soil. This is explained by the relative size of the different particles (clay, sand and silt) that soil contains. Clay particles are very small but, because this allows more particles to fit  in any given  space (say 1cm cubed), they have huge surface area  that dominates the physical properties of soil. In comparison, sand and silt particles are  larger, so fewer particles are needed  to fill a space  (say 1cm cubed again). As a result,  the overall  surface area of sand and silt is smaller and  so much less influential on determining the characteristics of a soil than the clay particles.

The source of this information and more details can be found on the RHS website

www.rhs.org.uk/advice in May