If you have clay soil in your garden, you may find that rain and stormwater aren’t soaked up very quickly and volumes of water may create puddles on the surface. This makes it very difficult to ensure healthy growth for plants, flowers and even lawns. Clay soil can also mean that you find it difficult to dig and work the soil before late spring, that you have to deal with water-logged areas and that plant roots find it difficult to penetrate and thrive in the ground. You will also find that the regular wet and dry periods you experience with other types of soil and disrupted. Creating a soakaway in clay soil can help to battle the problems associated with gardening in clay but is a much cheaper and less troublesome way of draining out excess moisture. Below we will show you how to make a soakaway in clay soil quickly and using affordable materials.
What is a Soakaway?
A soakaway (also spelt soak-away) is a type of drainage system that collects and disposes of excess water by directing it into the ground. Soakaways are often used in areas where there is a high water table or where the soil is not able to absorb water quickly enough. They are typically constructed out of perforated pipes that are buried in a trench, and the excess water is allowed to slowly seep out and into the surrounding soil.
How to Create a Soakaway in Clay Soil?
Creating a soakaway in clay soil is a task you can take care of on your own without needing to contact a professional gardening or building service. You will need to dig a hole in the ground which is then filled with rubble or gravel and some pipe trenches in your soil that extend across your garden. The rubble or gravel will help the water to pass through the clay soil and be carried downwards rather than remaining logged in the top layers.
What You Need
- A heavy-duty large garden spade
- Rubble or gravel from your local builder’s merchants
- Perforated plastic pipes
- Heavy-duty landscaping fabric
Step 1 – Prep
Your first step in working out how to build a soakaway in clay soil is to decide how large your garden soakaway drainage system will be. This will let you know how much gravel or rubble and perforated plastic drainage pipes you will need to buy from the merchants.
As a rule of thumb, you will need to dig a trench of about 1.8 meters deep which goes beneath the clay. You will also need to dig drainage trenches in the soil and place these every 3 to 6 meters across the garden. These trenches should be sloped so that they will be slightly skewed so that the water gathered will flow down towards your soakaway.
Step 2 – Dig the Soakaway Hole in your Garden
Dig your soakaway hole in the lowest part of the garden so that the water caught in the drainage pipes will naturally flow down towards it. You should also make sure that it is at least five meters away from any buildings in order to make sure that rainwater isn’t directed towards the foundations.
When digging the hole, you need to ensure that you dig deep enough in the soil so that you hit the ground beneath the clay level. Once you have dug the hole, you should cut down and place the landscaping fabric so that it lines the hole. This will keep the earth from becoming mixed up with the gravel and allow water to clog the hole.
Note: Depending on the size and depth required, you may need to hire a mini-digger and a driver to do this part for you.
Step 3 – Dig the Trenches
The next step is to dig your trenches across your garden for drainage pipes (Amazon link – opens in a new tab). You should make sure to measure the pipes ahead of time to ensure that the holes you create are wide enough.
You should also make sure there is enough of a slope leading down to the soakaway to ensure that collected water will flow down. As discussed above they should be dug across the entire space of the garden at a rate of one every 3 to 6 metres. You will need to dig the trenches so they connect at the bottom of the garden and will guide the collected water so that it flows into your soakaway.
Step 4 – Lay Your Drainage Pipes in the Trenches
Once you have dug the trenches you can lay down your perforated pipes, tidy up and ensure that they are all at an adequate slope and position to allow water to flow into your soakaway.
When you are certain of their positioning and that you have got the slope right, you should place a layer of about 2-3cm of gravel or small rubble into the pipes. Then place the topsoil and leave the ground to settle for about two weeks before you begin to landscape with turf and plants.
Step 5 – Add Gravel and Complete the Soakaway
Fill the soakaway hole with gravel or rubble up to the point that the layer is about 2cm away from the surface of the hole. Then out a layer of your landscaping fabric across the surface.
Then place your topsoil above the gravel layer. You should fill in the hole so that the soil sits slightly above the surface as this will drop down a little as the ground begins to settle. As with your pipe trenches, allow two to three weeks before you apply any turf, seeds, or landscaping to the area.
How to Fill a Soakaway?
- Add a Layer of Coarse Stones: Fill the bottom of the hole with a layer of coarse stones or broken bricks, about 10-15 cm deep. This provides initial filtration and aids in water distribution.
- Fill with Gravel or Crushed Stone: Continue filling the hole with gravel or crushed stone, leaving about 30 cm from the top. These materials facilitate the drainage of water into the surrounding soil.
- Top with Geotextile Fabric: Place another layer of geotextile fabric over the gravel or stone. This prevents the topsoil layer from mixing with the stones below.
- Cover with Soil: Fill the remaining 30 cm with the excavated soil. Tamp it down to ensure it’s compact.
- Plant Grass or Ground Cover: To integrate the soakaway into your garden, you can plant grass or other ground cover plants on the topsoil.
Alternatives to a Soakaway in Clay Soil
If you don’t like the idea of applying drainage trenches and a soakaway to your clay soil garden. There are some alternative drainage options you could try.
- You can save time and effort by using a prefabricated drainage box rather than creating your own gravel-filled hole
- You can install a drainage pipe system that will actively work to direct water down away from the surface
- Try to improve the drainage in your soil by adding grit, gravel, crushed stone, and organic matter to the clay. This will help to break up the clay a bit and hopefully improve the soil’s ability to drain excess water from the surface
Dealing with clay soil in your garden can become very frustrating for gardeners and unfortunately, there are no super quick and easy fixes. Your two main options are to either attempt to change the consistency of the soil by adding in other materials or dig beneath the ground to install a drainage system that will direct rainwater away from the surface. But you will find that your efforts are most definitely worth it, and your plants and flowers will benefit from being planted in soil that supports their growth and allows your garden to flourish.
Garden Doctor Tips
“Hiring a mini-digger with a driver will usually cost between £80-£200!”
“Aim to dig your soakaway at the lowest point in the garden to assist with drainage!”
“If you know anyone in groundwork construction – enlist their help for other ways to improve drainage!”
“Always direct the water away from your house. Never attempt to drain the water towards your foundations!”
Frequently Asked Questions
What is the depth of clay soil?
The depth of clay soil can vary depending on the climate and the geological features of an area. For example, in areas with a hot and dry climate, clay soil might be only a few inches deep. In contrast, in areas with a more humid climate, clay soil might be several feet deep because it has been deposited over time by water runoff.
Should I dig out clay soil?
Whether or not to dig out clay soil depends on your intent and what you want to grow. If you are looking to improve the soil, then adding organic matter (compost, mulch, manure) will be more beneficial than clay. Clay does have some benefits such as being a good moisture retainer and providing some nutrients. However, it can also be dense and hard to work with and can slow down drainage.
What is the major problem with clay soil?
Clay soil is a problem because it is dense and does not allow water or air to penetrate. This can cause problems with drainage, and the lack of air can also lead to anaerobic conditions which are harmful to plants. Additionally, clay soils can be hard to work with and can be difficult to cultivate.
Trevor Wright is not just a seasoned horticulturist; he’s the esteemed Garden Doctor. With a BSc in Horticulture and years of hands-on experience in the soil, Trevor has become a trusted mentor for all things gardening. As the founder of Garden Doctor, he’s committed to clarifying the intricacies of gardening, offering straightforward advice that’s rooted in years of practice. His writing is a garden of how-tos, savvy insights, and comprehensive guides that enable individuals to nurture and grow their garden dreams. When he’s not knee-deep in garden beds, Trevor is at his keyboard passing on his green-thumbed wisdom to budding gardeners, ensuring that the legacy of sustainable and joyful gardening blossoms far and wide.