Use this guide if your soil is sticky when wet, cracks in summer and puddles stay for days after rain. You will need a spade or fork, boards to stand on, and plenty of bulky organic matter such as garden compost or well-rotted manure.
Step by step
Check how bad the drainage is
Dig a hole about 30 centimetres deep, fill it with water and see how long it takes to drain. If water is still there the next day, drainage is poor. Note where water collects, especially near the house.
Work only when conditions are right
Avoid digging or walking on clay when it is wet, as this squeezes out air and makes it worse. Wait until it is moist but crumbles in your hand. Stand on boards to spread your weight.
Add plenty of organic matter
Spread a thick layer of garden compost, well-rotted manure or soil conditioner over the surface. Fork it into the top layer, or leave it on top as a mulch for worms to work in. Repeat every year, as the benefit builds up over time.
Avoid adding a little sand
Small amounts of sand mixed into clay can make it set harder. If you want to open up the soil, use large amounts of coarse horticultural grit only in small areas, such as planting holes for plants that need drainage. Organic matter is the main fix for most gardens.
Raise the growing level
For vegetables and plants that dislike wet roots, build raised beds filled with a mix of topsoil and compost. Plant slightly proud of the surrounding soil on heavy ground. Choose plants that thrive on clay for wetter areas.
Get advice for serious waterlogging
If water stands for long periods or threatens buildings, a drainage system such as a French drain or soakaway may be needed. These must lead water away from buildings, not towards them, and soakaways are normally placed well away from foundations. Ask a landscaper or drainage specialist, and check with your local council's building control if the work is near the house.
Ready-to-use checklist
- Drainage tested with a water-filled hole
- Wet areas noted
- Soil worked only when crumbly
- Boards used to avoid compaction
- Thick layer of organic matter added
- Plan to repeat organic matter every year
- Raised beds considered for vegetables
Practical tips
- Autumn is a good time to spread organic matter over clay, as winter weather and worms help break it in.
- Keep permanent paths in the garden so you are not walking over growing areas.
- Many roses, fruit trees and shrubs grow well on clay once it is improved, as it holds nutrients well.
Common problems
The soil sets like concrete in summer.
This is typical of clay low in organic matter. Keep it covered with mulch to reduce cracking and continue adding compost each year.
Water is pooling against the house wall.
Check that gutters and downpipes are clear and flowing into a working drain. Make sure garden soil is below the damp-proof course, and get a professional to look at drainage if pooling continues.
Plants rot over winter in heavy soil.
Wet cold roots are the likely cause. Replant in raised areas or containers, add grit to planting holes for those plants, and choose varieties suited to heavy soil.