How To Garden With Clay Soil

Don’t despair if the clay soil in your garden waterlogs in winter and dries to concrete in summer.

There are plenty of ways to work with a clay soil and not all of them as strenuous as my photo might suggest !

Help is at hand…..

 

 

This is my clay garden that has had many improvements both small and large over 10 years.

It used to waterlog in winter across the lawn and along the north boundary. The small original beds dried out in the summer sun. I tackled the problems systematically, dealing with the worst first. This was the extremely waterlogged north facing border in the shade of a 2m high fence….

 

 

 

Recipe for soil……

Garden soil is made up of a number of different components all of which are essential for healthy plant life….

1.Crumbs of rock or mineral particles  (Clay/silt/sand in various proportions)

2.Organic matter (decomposed plant and animal remains…compost/bark chips/leaf mould/well rotted manure)

3.Living organisms (worms/fungi/bacteria helping to break down organic matter)

4.Water (Containing minerals)

5.Air  (Plant roots need oxygen as well as water to survive, that is why plants suffer when the soil is very waterlogged or compacted…as there is no room for the air and they suffocate!)

The combination of these 5 elements is known as the Soil Structure

Clay Soil – What it is made from

The crumbs of rock in our soil will make up about 50-60% of the total recipe and a clay soil will contain a majority of clay particles. These particles are very fine, much smaller than sand or silt. They become sticky and can be squashed together when wet, holding onto water more easily, which means they readily water log in wet conditions or bake in dry conditions. They also hold onto essential nutrients. When compacted by walking or driving, most particularly when wet, the particles squeeze together so tightly that the air is driven out.

The Texture of clay soil (which is the ratio of clay to sand and silt) is not readily altered, but the Structure of the soil is.  This is done by adding more of item 2 in the recipe above….Organic Matter. This will aerate the soil, improve the drainage and attract living organisms…all essential for a good healthy plants.

 

Solution 1 ….. Add organic matter

Dig over the ground to say a depth of 30 cm to 40 cm (double dig) and mix in as much organic matter as you can…10 cm depth would be a good start. The kind of organic matter that will work best to ameliorate a heavy clay soil is something not too refined such as bark chippings. Large grit particles are also good but the amount required would not be very practical except for small areas. If the clay is not too heavy then a mix of garden compost (home made or from garden centres or soil merchants) will also benefit. It is important not to work the clay soil when it is wet or waterlogged as this will compound it’s problems. Better to wait till until it is dry enough.

Clay soil often means water logging in winter, but it can also mean that the surface of the soil can dry to a hard pan in summer. This in turn will encourage the much needed summer rain to wash straight off. The addition of organic matter (which paradoxically helps retain water at the same time as aiding drainage)  will alleviate these problems. Make sure once the work is done that you add a further top layer of mulch (organic matter) so that the soil surface is easily watered and does not dry out.

 

Solution 2 ….. Make a raised bed

This can take many forms from simply mounding the soil in the bed by 20cm or more, to raising whole sections of garden or individual veg beds

This bed was raised by about 40cm with an imported sandy soil mixed with organic matter and some of our own clay soil. We simply sloped the bed from the front at a gradient low enough to suit most plants, rising up to 40cm. The grassed area behind (out of the picture) was also raised.

Establishing new plants on a slope risks water running straight off rather than soaking in, so we  made sure that there was always a good mulch layer(organic matter) on top, to aid watering and stopping the surface drying out.

 

 

 

 

Raised bed for ornamentals or vegetables. Here with three layers of stylized timber sleepers. One would be sufficient to raise the level by 15cm – 20cm.  For veg beds, this can become the ‘no dig beds’

 

 

 

 

 

 

 

 

This planting of Alliums, ornamental grasses and probably Agapanthus, taken at Arabella Lennox Boyd’s garden was gently mounded up to a height of about 25cm towards the back with a discrete timber support.

 

 

 

 

 

 

A very ornate and intricate raised alpine bed at RHS Harlow Carr. With this open aspect any self respecting alpine would feel at home here! I took this photo a few years ago when it had first been constructed…it would be interesting to see how it has matured.

 

 

 

 

Solution 3 …..

Locate structure and hard surfaces to areas with the most challenging clay soil conditions

 

Use this part of the garden to for a lovely outdoor seating area. Here we’ve covered the ground with a weed suppressant  and covered it with pebbles,using only plants that can tolerate a little extra water in winter (it’s amazing how much this poor Box has put up with) Pots can also add another dimension.

This was our north facing boundary.

 

 

 

 

The greenhouse occupies another area with challenging clay soil conditions. The light is good for growing plants here and the composts are hidden under the Prunus beyond

 

 

 

 

 

 

 

Solution 4 …. Dig up and replace some of the clay soil.

 

A good, if strenuous solution for smaller beds where the soil is a solid sticky clay and particularly if it is gleying (grey-blue in colour) meaning it’s lacking oxygen. There is most likely to be  some usable top soil (say 10cm – 30cm) which you should dig up and keep to one side.

We dug out a few small borders in our own garden to a depth of 45cm, keeping the top 10cm, bagging up the worst of the clay for the tip , and replacing with a mix of sandy topsoil, garden compost and the original top soil.

 

 

This photo is taken 10 years after the original bed prep. The Verbascum bombysetiferum in the foreground (behind Suki) and silvery leafed Stachys byzantina (furry lambs ears) normally associated with Mediterranean dry gardens grow happily along the border edge.

The lavender on the left of the picture is in an original low raised bed….some plants you just can’t please……they hate the winter wet !

 

 

 

 

 

Solution 5 ….. Install some drainage

There are many different methods of draining the ground, some more simple than others. The simplest are open ditches but mostly not suitable for domestic gardens.

French drains, which are open ditches back filled with course gravel and topped with a membrane and topsoil can be effective. Pipe drains are more commonly used.

Pipe drains are perforated plastic pipes laid in trenches to a depth of about 40cm/60cm on a 5 cm bed of course gravel to a gradient of 1:40 . It is then back filled with 10 cm of gravel and covered with topsoil. A single one or two drain runs can easily be achieved yourself, but if the area is large or complicated, it would be best to seek advice from a landscape or specialist contractor.

If you tackle it yourself, first identify the area towards which you are going to drain such as a natural ditch, watercourse or soak-away. The perforated flexible pipes are obtainable from good builders merchants.

 

 

 

 

 

 

 

 

 

Solution 6 ….. Accept your soil and make the most of plants that like wet conditions

There are many plants that thrive in wet conditions. Select a few and let them do their job.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

For a list of clay loving plants take a look at my September blog

 

Alternatively try designing a Bog Garden…visit RHS website for some ideas