Border plants for clay soil

Clay is hard work to start with. It holds water and nutrients better than any other soil, so an established border on clay needs less feeding and survives a dry August better than the same border on sand. Getting to established is the difficult part, because clay is cold in spring and sets hard in a drought.

How to tell it is clay

Take a handful from a spade's depth, wet it and roll it. Clay rolls into a sausage without breaking and takes a shine when you rub it with your thumb. In a dry summer the surface cracks into plates, and cracks wide enough to lose a trowel down mean heavy clay. Clay also warms weeks later than sand, so seed sits and rots and everything comes through late.

Improve it, but choose plants that like it first

Do both, and in that order. Mulch with 5 cm of compost or well rotted manure every autumn and let the worms take it down, because digging it in does less good and damages the structure while you are at it.

Since the improvement is slow, choose plants content with clay as it is now and let the mulching happen in the background. There are a great many of them, which is why the clay soil list is one of the longest on this site.

Wet clay and clay that bakes

The same bed can be both, six months apart, and the swing is what kills plants. Winter wet rots the crown of anything expecting drainage, and the summer setting shears roots that never got down deep enough.

If your bed sits wet all winter, lean on the ones that take real damp. Dogwood 'Midwinter Fire' (Cornus sanguinea 'Midwinter Fire') at 200 cm (2 m) each way flowers May and June and earns its place with its winter stems. Knotweed 'Firetail' (Persicaria amplexicaulis 'Firetail') is 120 cm by 90 cm for July to October. For April into June, Snake's Head Fritillary (Fritillaria meleagris) at 30 cm and Camassia (Camassia leichtlinii) at 90 cm both want clay that stays damp.

The back of the bed

Shrubs are the easy part, because the soil that frustrates fussy perennials is what most big shrubs want. English Holly (Ilex aquifolium) is 400 cm (4 m) by 300 cm, evergreen and flowering May and June. Guelder Rose (Viburnum opulus) at 400 cm by 400 cm flowers May and June and carries red berries afterwards. Ebbing's silverberry (Elaeagnus x ebbingei) at 350 cm by 300 cm is evergreen and flowers in October and November.

English Yew (Taxus baccata) at 400 cm by 300 cm is the one people assume will not take clay. It does, as long as the ground is not actually waterlogged, and a clipped yew backdrop flatters everything in front of it.

The middle band

Japanese Anemone 'Honorine Jobert' (Anemone x hybrida 'Honorine Jobert') is 120 cm by 90 cm, flowers August to October, and runs about once settled. New England Aster 'Harrington's Pink' (Symphyotrichum novae-angliae 'Harrington's Pink') at 130 cm by 60 cm flowers September and October and wants the moisture clay holds in late summer. Crocosmia 'Lucifer' at 120 cm by 60 cm flowers July and August from corms that bulk up into a thick clump. Culver's Root 'Fascination' (Veronicastrum virginicum 'Fascination') is 150 cm by 60 cm for July and August.

Hydrangea 'Endless Summer' (Hydrangea macrophylla 'Endless Summer') at 120 cm each way suits an east or west-facing clay bed and flowers June to September.

The front edge

Hardy Geranium 'Rozanne' (Geranium 'Rozanne') is 50 cm tall and 100 cm across, flowering June to October. Lady's Mantle (Alchemilla mollis) at 45 cm by 60 cm flowers June to August. Bergenia 'Purpurea' at 45 cm by 60 cm is evergreen and flowers February to April, so the front has something in it in the worst month of the year.

Avens (Geum 'Totally Tangerine') at 90 cm by 45 cm runs May to September, and Yarrow 'Cerise Queen' (Achillea millefolium 'Cerise Queen') at 60 cm by 45 cm covers June to September and holds up where the clay dries hard. For the very end of the season, Crimson flag lily 'Pink Princess' (Hesperantha coccinea 'Pink Princess') at 60 cm by 45 cm flowers September to November on damp clay.

Planting into clay without digging a sump

Dig the hole with a fork rather than a spade, and rough the sides up. A spade in wet clay polishes the walls into something close to a ceramic pot, water collects in it, and the plant sits in standing water.

Plant slightly proud, with the top of the rootball a centimetre or two above the surrounding soil, because clay settles and a plant set dead level ends up in a saucer by its second winter. Do not put compost in the planting hole either. It makes a soft pocket the roots stay inside, so the plant never anchors. Improve the whole bed on top instead.

Then mulch, which stops the surface cracking and stops rain hammering bare clay into a crust. Autumn planting suits clay better than spring, unless the bed is genuinely waterlogged over winter, in which case wait, because a new plant standing in cold water for four months will not be there in April.

Sun or shade changes the list again

Clay in full sun and clay in shade share the soil problem but take different plants. The sunny version takes most of the big flowering perennials, and that list is at clay in sun. The shaded version is ferns, hellebores and the woodland end of the catalogue, at clay in shade.

Border Builder does this for your own bed: enter its size, aspect and soil and it draws up the plan.