What actually grows well in heavy clay soil?

Choosing plants for clay is much easier once you know what clay actually offers: plenty of nutrients, plenty of water, cold slow warming in spring, and very poor aeration in winter. Almost every failure on clay is a plant that evolved on thin dry soil and cannot tolerate wet roots in January.

Step by step

1. Confirm what you have.Wet a handful and roll it. Clay rolls into a sausage and takes a polish. It also cracks in drought and sticks to boots in winter.
2. Use the reasoning, not just the list.Ask where the plant comes from. Moist meadow, woodland edge, riverside and hedgerow plants suit clay. Mountainside, cliff, scree and Mediterranean hillside plants do not. That question answers most cases.
3. Plant shrubs and trees that suit it.Cornus, viburnum, philadelphus, weigela, ribes, hawthorn, crab apple, rowan, birch, hazel, amelanchier, hydrangea, chaenomeles, mahonia, spiraea and most of the shrub roses.
4. Plant perennials that suit it.Hardy geraniums, astrantia, hellebore, persicaria, sanguisorba, rudbeckia, helenium, aster, phlox, monarda, ligularia, hosta, day lily, aconitum and Japanese anemone.
5. Grow roses, which are famously happy on clay.The nutrient-holding capacity of clay suits them very well. It is one of the few soils where roses need less help rather than more.
6. Choose grasses and ferns for texture.Molinia, deschampsia, calamagrostis and most ferns cope well. Stipa tenuissima and the drought-adapted grasses generally do not.
7. Know what to avoid.Lavender, rosemary, cistus, santolina, most silver and grey-leaved plants, sedum in quantity, bearded iris, most alpines, and tulips as a permanent planting. All of them rot in winter wet.
8. Plant in autumn or spring, never into wet clay.Working clay when it is wet smears and compacts it and the damage lasts years. Wait until it crumbles rather than smears.
9. Plant high and wide rather than deep.Dig a wide shallow hole rather than a deep narrow one, break up the sides so roots can get out, and set the plant slightly proud so it is not sitting in a hollow that collects water.
10. Do not dig a compost-filled hole in solid clay.It becomes a sump that fills with water and drowns the plant. Improve a wide area, or the whole bed, rather than one planting pit.
11. Mulch every year and let the worms do the work.Fifty to eighty millimetres of compost or well-rotted manure on the surface each autumn is what genuinely improves clay over time. It is slow, it is cumulative, and it works.
12. Grow the difficult things in raised beds or pots.If you want lavender or Mediterranean herbs, grow them in a raised bed or a gritty pot rather than fighting the soil. That is a far smaller job than converting a border.

Tips

• Clay is the soil most gardeners end up grateful for. Once the structure improves it grows things better than light sandy soil does.
• If a plant description says it needs sharp drainage, believe it and put it in a pot.
• Watch what thrives in neighbouring gardens and hedgerows. It is the most reliable plant list available, and it is free.

Common mistakes

• Adding sand to improve clay — In anything less than enormous quantities it produces something closer to concrete. Bulky organic matter is what improves clay structure.
• Planting lavender and Mediterranean herbs in a clay border — They rot over the winter rather than dying of anything obvious, so people replace them repeatedly. Grow them in a pot or a raised gritty bed.
• Digging when the soil is wet — It smears and compacts, and the damage takes years to reverse. Wait for it to crumble.
• Planting too deep — A hollow around the stem collects water in winter. Set plants slightly proud of the surrounding level.

Questions people ask