Soil can be wet because it is compacted, or because of a high water table, where the upper level of the ground water is near the soil surface. Clay soils are wet in winter and baked dry in summer. Unless you install drainage, you will need to work with your soil and choose plants adapted to wet conditions.
Wet soils: plants for
There are many plants which will grow successfully in soils which are permanently moist, but few will survive long spells of flooding or waterlogged conditions, especially in summer. The ones listed here are more tolerant than most.
Plants like clay a lot more than gardeners do. I feel rather smug about my sandy soil, which is light, easy to dig and drains freely.
However, when I see how well so many plants look growing on clay my attitude changes. Clay soils might be heavy to work and a bit challenging, but they are fertile and lend a good deal of support and anchorage.
Many shrubs grow well on clay soils, especially the popular deciduous flowering shrubs: deutzia, philadelphus, weigela, forsythia and ribes for example.
The level of nutrients in the soil means that supplementary feeding is rarely required for good flowering and performance. However, I would still recommend an annual feed with a slow-release general fertiliser for best results.
On heavy clay shrubs are a natural choice because major cultivation of the soil is rarely required after planting, just the removal of weeds around the plants.
An occasional mulch of composted bark, garden compost, or well rotted manure will benefit the plants and gradually improve the soil structure.
Roses love clay, as do many other members of the rose family such as pyracantha and cotoneaster. The larger growing shrub roses planted with informal evergreens, such as Cotoneaster franchettii and Pyracantha ‘Teton’ are ideal in country gardens with a bit of space.
With all year round interest a combination of this type makes a good screen or backdrop. I do encourage gardeners to think of shrub roses just as they would any flowering shrub and to use them accordingly.
Rosa ‘Bonica’ for example has healthy green foliage, few thorns and will bloom repeatedly though summer and into autumn with little attention from you. Growing it on a clay soil means that its even lower maintenance.
The vigorous shrub Leycesteria formosa grows just about anywhere and succeeds well on clay, even on damp sites. The tall arching, hollow stems are sea-green.
The flower clusters hang from the branches from early summer through to autumn, claret red bracts interspersed with small white flowers.
These are followed by shining purple fruits loved by pheasants, hence the common name: “Pheasant Berry”. Look for the variety Golden Lanterns with soft golden yellow leaves. It’s perfect to brighten up a shady corner.
Leycesteria is ideal to plant with red-barked dogwoods. All cornus grown for their winter stems do well on clay and are also valuable for sticky, wet sites.
A combination of these two plants with symphoricarpus, the snowberry is ideal where gardening is impossible, on a heavy clay bank for example.
When it comes to evergreens those hardy favourites come to the fore: choisya, aucuba and Viburnum tinus. All of these do well in sun as well as shade and provide important structure on the heaviest of soils.
Mahonias also do well on clay and provide cheering winter and early spring colour. Their yellow flowers combine well with the golden variegations of spotted laurels.
Clay soils are often neutral to acid and in these conditions the hardy hybrid rhododendrons will thrive. R. ‘Cunningham’s White’ is an old variety with dark green foliage and the palest mauve flowers that fade to white.
It is incredibly hardy and will even tolerate slightly alkaline conditions. For a dark red ‘Nova Zembla’ is a great choice: upright growth with deep red, weather resistant blooms.
All deciduous magnolias grow well on clay. For smaller gardens Magnolia stellata is the natural choice and it performs reliably with a wonderful display of starry, shining blooms from early spring. The grey, catkin-like buds are attractive in winter.
For larger spaces choose one of the cultivars of Magnolia soulangeana, however this grows best in neutral to acid clay.
For late summer flowers the hardy hibiscus are reliable, even if they are late to break into leaf at the beginning of the season. They grow well on clay, the foliage stays green and healthy and the flowers can be superb. Hibiscus syriacus ‘Hamabo is one of the best.
Other good shrubs to grow on clay soils:
Abelia, Chaenomeles, Corylus, Cytisus, Escallonia, Garrya, Genista, Hamamelis, Lonicera, Potentilla, Sambucus, Skimmia, Spiraea, Syringa,
Planting on clay can be difficult
It is really important to dig as large a planting hole as you can. Mix plenty of planting compost with the soil before you replace it around the plant to acclimatise the roots to their new home.
Clay soils can dry out and bake hard in the summer. Early autumn is therefore the best time to plant, to give the shrub longer to establish. Planting in spring may be difficult if the ground is wet and heavy.
Do remember that shrubs grown on clay have great stability, the weight of the soil keeps the roots firm and the plants rarely suffer from wind-rock. When shrubs are established little further maintenance or cultivation is needed.
A well known gardener said: “If you have free draining acid, sandy soil, plant rhododendrons; if you have chalk plant clematis; if you have clay move!”
What he should have said was: If you have clay, you will have to make the best of it by choosing the right plants.