Complete guide to clay soil

Use our guide to find out how to manage clay soil in a way that enables you to garden better, and learn to see your clay soil as an opportunity, rather than a hindrance.

What is clay soil?

Clay soil is defined as being rich (at least 30 per cent) in fine clay particles. They tend to be heavy to work, take longer to warm up in spring, drain slowly after rain, are easily damaged when walked on and can be wet and slimy to handle. However, clay soils are also rich in nutrients, hold on to more water in a drought and support a range of hungry plants. If you manage your clay soil well, you can have a beautiful garden that doesn’t need watering or feeding as much as other gardens. They key to managing clay soil is to grow suitable plants, add drainage where necessary and help to break up the fine clay particles.

How to find out if you have clay soil

Take a handful of soil and roll it into a ball. If it’s clay, it will roll easily, feel smooth but also slightly sticky. If you then roll it into a sausage it will again roll easily without cracking. The heaviest clay soils will then become shiny if you rub the surface.

Tips for working with clay soil

Only walk on, or work clay soil when it's dry. If worked or walked on when wet, clay soils lose their structure and become puddled and compacted. This can then take a long time to fix. If you need to work wet soil for sowing or planting, for example on an allotment or veg patch, you can cover areas with plastic sheeting. This will prevent rain from penetrating the soil, which can help it to dry out and make it workable.

However, remove any covers if frost is forecast, as frosts help to break up large clay pieces. Traditionally, clay soil was dug into narrow ridges, which helped expose the clay to frost.

Sow seeds later in spring than is conventionally advised, or start them indoors to plant out after all risk of frost has passed. You can also use cloches or clear plastic to warm soil up sooner, which can take up to six weeks. Use a soil thermometer to find out what temperature your soil is before sowing – most seeds won't germinate if soil temperature is below 7ºC.

If planting shrubs and trees, plant them on slight mounds so their roots don't sit in waterlogged soil. If planting perennials, throw gravel into the planting hole to aid drainage.

Use stepping stones on lawns with heavy soil to prevent compaction.

Make raised beds to aid drainage and to reduce compaction. Make sure the beds are small enough so you can reach the centre from either side, so there's no need to stand on the soil.

Consider adopting a ‘no-dig’ approach to growing, which involves adding layers of organic matter over cardboard each year to suppress weeds, and sowing direct into the organic matter. This works well on clay soils, especially in raised beds.

How to improve clay soil

Dig in plenty of bulky organic matter such as home-made compost, well-rotted manure or composted bark, as this opens up the structure of the soil and makes it much easier to work.

Apply organic matter as a mulch around trees and shrubs, to conserve moisture and stop the soil drying out in summer.

You may want to experiment with adding calcium, lime or gypsum to the soil. Different clay soils respond to these minerals differently, but all can help to 'improve' soils to make them more workable, and can help to break down clay soils faster then other measures. Always test a small area first, to see if it works on your clay soil. Most clay soils are alkaline, but for acidic clay soils, adding lime can reduce the pH, which can help prevent the clay particles from sticking together.

Adding sharp sand, or grit to the lawns on clay soil can make them less susceptible to compaction, while adding stepping stones can reduce footfall on the lawn itself. Elsewhere in the garden, adding grit and sharp sand to clay soil can make it easier to work but this is not as effective as adding organic matter.

Plants for clay soil

Many plants work well in clay soils, thanks to its high nutrient content and water retention. Browse our list of features on which plants to grow in clay soil, from flowers to trees and shrubs.

• Flowers for clay soil
• Five plants for a clay soil border
• Trees and shrubs for clay soils

Frequently asked questions

Which plants can I grow in clay soil with poor drainage?

If you have really poor drainage it's best to try and improve this by digging to loosen the soil, adding grit to the base of plant holes so plant roots don't sit in water, and mulching annually with composted bark, which helps to break up clay soils. Then choose plants that thrive in wet soils such as dogwood, loosestrife, hemp agrimony, apples, hollies and roses.

How can I improve drainage in a clay soil lawn?

Aerate the lawn by using a fork or core aerator to loosen compacted soil and create holes in the lawn. This will relive compaction and aid drainage. On very soggy soils you can fill the holes with horticultural grit, sand or gravel, which will create more permanent drainage channels and help keep the lawn dry. If the lawn remains boggy you may consider digging a drainage ditch to one side, and using French drains beneath the lawn to channel water into it.