Clay soils

• Overly wet and waterlogged in winter
• Very dry, “concrete-like” in summer
• Large cracks in soil
• Plants wilting

Clay is an important mineral constituent of all good soils, along with sand and silt. But when it is the major constituent, the soil is called a clay soil; clay soils contain more than 30% clay. Because clay particles are small and fine and clump together in large numbers, clay soils are regarded as being “heavy”.

It may be obvious that you have a heavy clay soil, in that you can see large clods or clumps of soil that are difficult to break up. The soil becomes overly wet or waterlogged in winter and dries out to something resembling concrete in summer.

How do you tell if you have a clay soil? Take a small piece in your hand.

• Clay soils feel slightly sticky
• They feel smooth when rubbed between thumb and forefingers
• They can be rolled into a ball and into a sausage shape without cracking
• The moist surface becomes shiny when rubbed

Clay soils are innately fertile, as the clay particles hold on to nutrients. They also contain a lot of beneficial microorganisms, and other soil flora and fauna, adding to this innate fertility. A good, well maintained and prepared clay soil is the best soil you can have because of this fertility and just about all plants will grow very well in them.

They clay particles hold moisture well too, so don’t dry out quickly in summer.

Depending on the parent rock from which they originated, clay soils are either alkaline, neutral or acidic.

Very heavy clay soils may have very poor drainage, especially where areas of very compact soil (known as “pans”) exist. This means they become very wet or even waterlogged in winter and during periods of prolonged wet weather. Most plants won’t grow well in waterlogged soil.

Clay soils are also difficult to cultivate when they’re overly wet or very dry, and slow to warm up in spring, delaying any seed sowing.

Dry clay soils can crack open – sometimes with deep fissures – in summer when dry. This can lead to severe root damage.

Clay soils also “cap” in wet weather or periods of heavy rainfall, forming a hard crust on the soil surface.

While just about any plant will grow in a well-prepared, good clay soil, the following are particularly suitable, especially in very heavy clay soils.

Trees
Acer
Amelanchier
Betula
Crataegus
Eucalyptus
Laburnum
Malus
Pyrus
Sorbus

Shrubs
Aucuba japonica
Berberis
Buddleja
Chaenomeles
Cornus
Cotoneaster
Deutzia
Escallonia
Euonymus fortunei
Forsythia
Fuchsia
Garrya elliptica
Hydrangea
Hypericum
Ilex
Kerria japonica
Lonicera
Mahonia
Philadelphus
Potentilla
Pyracantha
Ribes
Rosa
Spiraea
Syringa
Viburnum
Vinca
Weigela
Conifers
Araucaria araucana
Chamaecyparis lawsoniana, C. obtusa, C. pisifera
Ginkgo biloba
Juniperus
Picea
Taxus
Thuja plicata

Herbaceous perennials
Alchemilla mollis
Anemone
Aruncus
Aster
Astrantia
Bergenia
Campanula latiloba
Carex
Digitalis
Epimedium
Geranium
Geum
Helleborus
Hosta
Kniphofia
Lamium
Ligularia
Papaver
Persicaria
Phlox
Primula
Rodgersia
Sedum
Solidago