Stop, don’t panic! No need to tear out your hair over heavy clay soil, which is often seen as the gardeners bane! Clay soil doesn’t have to be a nightmare requiring huge amounts of soil improvements, instead we can create some wonderful gardens by working with the soil types we have, observing and working with nature and studying what plants grow in native clay soils.
Some of the worlds most spectacular gardens were actually created on heavy clay soils; places such as RHS Garden Rosemoor and Hyde Hall work with the clay conditions to create magical gardens.
Often attempts are made to improve clay soils by adding sand, grit, or gravel, this can be done with limited short term success in small areas, but to dramatically change the properties of clay you would need 250 kg of sand/gravel per square metre of clay soil! So instead of fighting your clay lets work with it by planting trees/shrubs/perennials which like clay. Fruiting trees such as apple, cherry and plums love clay soil and will produce copious amounts of fruit whilst items such as strawberries and raspberries are harder to cultivate on clay.
Your clay soil should have pathways created, so as to avoid compacting clay soils and walking over wet clay. This does mean that working on clay soils during the wet winter months should be avoided at all costs. If you must grow crops which do not work well in clay (such as root crops) then creating a series of raised beds with inter-joining walkways means you can grow more produce without damaging your soil.
What are the properties of clay soil?
- Smallest particles out of clay, silt or sandy soil (less than 0.002 mm)
- Good water storage properties
- Due to small particle size it has a tendency to settle together and limit air movement
- Slower to drain and locks up nutrients (thus being rich in plant nutrients)
- Very chemically active (good nutrient bonding)
- The cation exchange properties of clay allow for good water and nutrient retention
- Heavy; cold and tends to be water logged
- Low AFP (air filled porosity)
- Difficult to work, wet and sticky in winter and bakes hard in summer
- Slower to warm up (due to texture and water retention)
Soil type comparison
|Water retention||Sandy soils do not retain water well||Good water retention||Clay soils retain water well but are prone to getting water logged||Has good water retention due to addition of clay|
|Nutrients||Sandy soils are inert and have low cation exchange capacity||Low cation exchange capacity meaning it does not hold on to nutrients||Clay soils have a high cation exchange capacity meaning they hold onto nutrients well||Has relatively good cation exchange capacity due to the addition of clay|
|Warming||Sandy soils have low water retention making them faster to warm up than clay soils||Relatively slow to warm due to water retention||Clay soils are heavy and retain water, as such they are slow to warm up||Medium warming (not as fast as sand but faster than silt and clay)|
|Cultivation||Sandy soil is advantageous for growing root crops such as carrots; where problems such as Phytophthora won’t effect your crop unlike planting root vegetables in clay based soils.
Sandy soils will warm faster than clay based soils due to less water logging, as such seeds can be planted out and germinate earlier.
|Can be easily compacted||Difficult to work due to clay soils being “sticky” and hard to work, also warms slower than sand/silt so the growing season for clay soils can start later (this is due to the high water retention of clay soils)||Easy to work with but can become harder when the mixture is higher in clay|
|Aeration and drainage||Sandy soils are very free-draining||Drains poorly and retains water longer||Clay soil is slow to drain and has low AFP (air filled porosity)||Drains well due to composition (sandy soil) and has good AFP|
|Additional information||Silty soil is very similar to clay soils|
* Loam soils are a combination of sand, silt and clay in almost equal proportions, due to this mixture it helps to remove the negative aspect of each soil type.
Examples of clay loving plants
Bellow is a small list of plants which can thrive on clay soils, ranging from fruit bearing beauties to spectacular flowering specimens.
- Bergenia cordifolia
- Viburnum tinus
- Physalis alkekengi
- Hydrangea macrophylla
- Hemerocallis (Day lillies)
- Digitalis purpurea
- Crataegus (Hawthorn)
- Malus (apple)
- Acer japonicum (Japanese maple)
- Cotoneaster horizontalis
- Lonicera japonica
- Juniperus communis
- Ginkgo biloba
- Thuja plicata
Next time we will explore more about soil types, structure and how to make the most out of your soil as we continue to explore a vital gardening topic.