Clay gardens have the potential to be one of the most productive gardens for vegetables, fruit and ornamentals.
Soils
Soil texture cannot be altered as it based on the parent rock. It is the composition of the soil in terms of the particle size. Clay soils have the smallest particles and sand the largest. As a comparison, approximately a 1000 million clay particles are needed to make the same volume as one sand particle.
Soil structure is the way in which the particles combine to form larger groups or aggregates. Because clay soil has such small particles, it has a much larger surface area allowing for other elements such as soil minerals to easily combine with it. This is more correctly known as cation exchange and is where the positively charged mineral ions are held in such a way by the negatively charged clay particles that they are still available to plants.
Gardening with Clay Soil
Gardening with clay soil has both advantages and disadvantages – and not all forms of clay are the same. For example, reddish clays usually has better aeration than blue/ grey clays. It may be useful to check one of the interactive soil maps available online to discover both the dominant type of clay soil and the bedrock in the area.
Disadvantages
- A clay soil does not drain well, which is why it gets waterlogged easily
- It is susceptible to damage when worked or walked on; when wet this can lead to compaction
- The small particles are the main reason why clay goes hard and cracks in drought conditions
- Clay soil warms up more slowly in spring than other soil types as it reacts slowly to temperature changes
- It is hard to dig, sticking to spades and boots when wet and coming up as large clods where the particles have stuck together
Advantages
- Most clay soils contain either high nutrient levels or the potential to be highly nutritious
- The addition of lime, Calcium carbonate, can aid the sticking together of clay particles to improve the soil structure. This is known as flocculation, or liming the soil. However, Calcium sulphate, Gypsum, is less likely than other forms of lime to alter the pH of the soil, so may be a better choice
- The addition of organic matter / humus / compost will also encourage the creation of these soil crumbs, or combination of soil particles
- A further benefit of organic matter is it improves the drainage of clay soils
Improving Clay Soils
Digging
- Rough dig the area in autumn leaving the soil in coarse lumps to be further broken up by the action of frost over winter. A fork is often better for digging clay soil than a spade
- Add sharp river sand and / or grit as well as organic matter
- Consider double digging a new area, incorporating sand, grit, humus
No-dig
- A longer term plan, involving, for example, adding layers of organic matter, cardboard, grass clippings etc to gradually improve the top layers of the clay soil by the action of worms and decomposition
- Perennial weeds should be removed first!
What to Grow in Clay Gardens
There a wide range of plants which can be grown in clay. And although soil is arguably the most important, it is worth remembering that there are other factors in keeping plants healthy, for example aspect (sun, shade).
Flowering Shrubs
The suggestions are in alphabetical order and between them will provide flowers for most of the year.
- Abelia
- Chaenomeles, ornamental quince
- Hydrangea
- Laburnum
- Lonicera periclymenum, honeysuckle
- Philadelphus, mock orange
- Ribes, flowering currant
- Roses
- Syringa, lilac
- Weigela
Herbaceous Perennials
A list of what doesn’t grow in a clay soil may actually be shorter! This selection offers foliage interest as well as flowers over a long season.
- Ajuga reptans
- Aster, Michaelmas daisy
- Bergenia
- Digitalis purpurea, Foxglove
- Gaura
- Geranium
- Helenium
- Hosta
- Japanese Anemone
- Lychnis coronaria
- Peony
- Persicaria
- Pulmonaria, lungwort
- Sedum
- Thalictrum
Annuals, Biennials, Bedding
- Coreopsis
- Myosotis, Forget-me-not
- Petunia
- Tagetes, French marigold
Bulbs, Corms, Tubers
- Crocus
- Galanthus, snowdrop
- Hyacinthoides non scripta, Bluebells
- Narcissus, Daffodil
The Kitchen Garden
Many vegetables prefer a clay soil, so it is arguably the best soil on which to start a kitchen garden.
If the clay is very heavy then raised beds are an idea solution for the kitchen garden. they may not be as practical in the ornamental gardens where borders may need to sweep around lawn edges.
To avoid walking on the soil of raised vegetable beds, make them no wider than 1.2m -1.5m (4ft -5ft) wide beds. This way they can be reached from the sides, as in from the paths which have been created between them.
Raised beds or improved soil is necessary for early vegetables and seed beds due to the coldness of clay soil.
Vegetables
- Beans
- Broccoli
- Brussels sprouts Cabbage
- Chard
- Lettuce
- Pak choi
- Peas
Potatoes and Jerusalem artichoke will also help break up the soil. And, so long as the soil has been enriched with compost, squash will do well.
Fruit
Many tree fruits and bush fruits that will happily grow in clay gardens as they prefer a slightly acid pH.
- Currants, including gooseberries, are tolerant of a clay soil.
- Apples other than those on M9 (dwarf rootstock) will manage with heavier clay soils, although both apples and plums are best on a free draining clay soil.
- Generally speaking the more dwarf or restricted the rootstock, the less able the fruit tree is to cope with a heavy, winter wet clay soil.
- Pears are more able to cope with damper soils over winter.
With all fruit trees and bushes, improving the soil in the planting hole is crucial. This should enable even peaches, olive and citrus to grow and crop on clay soils. Although they are best planted in a free draining spot or on a slope.
Finally, if there is a choice, go for a garden with clay soil as this is generally the easiest to turn into that elusive, fertile, friable ‘fine tilth’ much loved and dreamt of by gardeners throughout the ages.
Marie Shallcross
Plews Garden Design and Consultancy; Gardening Lessons