When I visit people in their gardens for a design consultation they often look at me with despair in their eyes, and apologetically admit they have Clay Soil. For most people clay soil is the bane of their gardening lives, limiting the type of plants they can grow, flooding in the Winter and cracking up in the Summer.
But do not lose hope! There are ways to work with clay and get the best out of it, as well as skirting round the problem.
What actually is clay?
You know if you have clay soil if you take a clod of earth from your garden and roll it into a sausage shape between your hands. Rather than it crumbling, if it keeps it’s shape and doesn’t crack, you have clay. If you then rub it and it becomes shiny, congratulations, you have heavy clay!
Clay is made up of minute particles that are many times smaller than a grain of sand. They have a thin plate like structure so you can imagine bread slices stacked on each other held in place by electromagnetic forces. Therefore they have a greater surface area then the surrounding soil. These particles easily stick together and tend to form great lumps as you will know when you put your fork in the soil in Spring and a great clod comes out in one go.
Soils with 30% minimum clay particles are considered clay soils. They are very easily damaged. Even walking on them a few times over Winter can compact them and make it hard for the gardener to then achieve a light, fluffy, workable soil.
Because they hold water, like a clay vase, they tend to get waterlogged easily. Who hasn’t lost free draining plants like Lavender over the Winter or waited for their Tulips and Alliums to come only to find rotten bulbs.
They are also slow to warm up in the Spring because they are still wet and their drainage can be painfully slow. On the plus side, because the clay is negatively charged it attracts and holds positively charged substances like potassium, magnesium and calcium, compared to a sandy soil which you have to continually top up with fertilisers. Clay can be either acidic or alkaline.
Working with Clay
The best way to break down clay is what farmers have done for centuries. Turning up the clods in Autumn and then letting the frosts break down the lumps. Once clay breaks down and plant material is added it has a greater tendency to keep aerated and looser.
Flocculation, where you add lime to the soil, is a chemical process which helps the clods of clay break down (don’t use at the same time as manure as you can then create ammonia gas).
Once with a client the clay was so heavy we removed the entire clay content down 40cm. After seeing 100 tonnes of clay removed and bringing in better top soil I will think twice about doing this again – but it did work and all the drainage problems were resolved. This would especially work if you had a small bed and you were desperate to grow free draining plants.
In the past we were encouraged to add grit or pea shingle to the clay. According to the RHS you would need to replace 50% of your soil with grit to make it properly workable. Obviously this is not going to be possible with most people’s gardens let alone factoring in the environmental impact.
Elevation is a solution that works well. There is the No-Dig method where rather than rotate the clay, you leave it in place and each year you add a generous layer of compost on top of the clay. Over time you build up the level of workable soil without disturbing the clay.
Raised beds – this is avoiding your clay altogether and building raised beds of brick, wood or stone. It works especially well for vegetable patches and at a raised height of 40cm you can hand select exactly the type of soil you want. Also a thick mulch around your plants in Summer can prevent your clay drying out too much (which creates those famous cracks in the ground). Lawns can become waterlogged with resulting moss domination but golf courses get around this problem by simply adding 15cm of sharp sand on top of the clay, then laying the lawn!
Woody fruit trees like apples and pears and generally most shrubs can live in clay, especially the larger wonder ones like Spirea and Ribes sanguine. Some medium sized plants they enjoy soil are Rodgersia, carex, Moilina, Ligularia, Hostas and Iris. Some ground cover examples are Bergenia, Alchemmila, Pulmonaria and Phlox.
In terms of climbers Clematis and Honeysuckle are happy in clay. Suitable bulbs are Daffodils ad Snowdrops but not Alliums or Tulips. Roses love the nutrients in clay and really thrive, as do wisteria hysteria, clematis and honey.
Using the Right Plants
Obviously clay occurs naturally so there are vast plant communities that happily live in clay which the gardener can select from.
Because the clay is rich in nutrients and holds moisture in Spring and Autumn there are many plants that thrive.
Early season vegetables struggle with the water logging in early Spring, but main crop vegetables can really thrive: potatoes, leeks, brassicas, pumpkin and squash, lettuce and chard. Soft fruit like strawberries and raspberries not so well.
In short, don’t let clay get you down. There are interesting ways to work with your soil without having to move house. And if you fancy a trip to Devon you can check out RHS Rosemoor Garden in Great Torrington which is built on clay and you will see what can be grown there. Hyde Hall Gardens in Essex is another heavy clay garden.
Places to visit
The National Garden Scheme is still running. Founded in 1927 the scheme encouraged people to open up their gardens to the public to raise money for the newly formed district nurses role in poor urban areas. It has moved on since then, from “a shilling a head” to raise over 20 million pounds for a variety of charities in the last 10 years.
If you go to the NGS website and type in ‘Sussex’ the dates you are free and you will find 36 gardens that are opening their gates in July though each garden is just open for a day or two only. Most serve tea and cakes.