Thanks for taking your time to read our information on how to improve soil drainage, which we have written for UK gardeners. The vast majority of people who search for this advice will most likely have a clay type of soil. We will widen that definition slightly and refer to it as wet soil.
Most soil will benefit from being moist, but when it is wet, it has a tendency to be waterlogged, and that is never a good thing to have in your garden. Lawns don't like it and neither do vegetable plots or plants.
There are a number of methods to help improve the drainage in your garden and we shall cover all of these options below.
How Wet is Your Soil? - The first consideration
This is really the first question to give some thought to. The reason to give this some serious thought is that some drainage solutions are very simple, whereas others require planning and often a large amount of work.
The good news is, that for most people, there is no big cost to fixing drainage, and it is more about how much time you can afford to solve the problem. Let's begin with looking at the condition of your soil.
Very Wet Soils
In extremely wet soils, where quite literally, pushing a spade into the soil causes water to come out, is always going to be the hardest to drain. For many years the recommended solution was to create a drainage system that used making a set of trenches and filling those with broken tiles or with rubble.
The reality is that, it has been proven that system doesn't actually work all of the time. This system is known as a French Drain, and is more suitable for farm areas or very large lawns. We have explained French Drains in more detail below.
This is a more common problem. For most of the year the soil and ground may feel soft and really only dries out properly in the late Spring and early Summer months. Usually this is after an extended dry spell. When there is heavy rain, then very quickly puddles will start to appear, and the lawn/garden starts to hold the water and flood.
There are a range of methods for dealing with that type of wet soil. We shall cover those below as there are a few options that work very well, and are pretty easy to achieve.
Soil that is clay like or heavily compacted tends to hold water or flood much easier than well worked soil. There are a few solutions for this, and we shall start with the first method, which is pretty simple to achieve. We have listed the various methods to improve soil drainage below, in terms of how easy they are to do, and also how long they will take to see results.
Aerating the Soil
Clay type soils or wet soil happens if the soil is compact and suffers from little to no air circulation. The soil binds together and becomes sticky. With lawns, grass will still grow on top of the soil, but it will be poor quality. When the rain comes, it only drains away slowly, and the grass will then start to hold water.
Inevitably moss and perhaps thatch starts to appear and you end up with a sponge like lawn.
One simple method worth trying is simply to get a garden fork, and when the ground is wet push the fork into the soil to allow the air into it. This helps drain the soil and allows it to breathe. You do have to go over all of the garden to get the best results, and it is back breaking work.
There are a few different methods for doing this, and it is certainly worth a try.
Double Digging for Drainage
If the aeration method doesn't work, then the next option is to double dig the garden, or at least the area that id flooding. The term "double digging" sounds like a whole lot of work, and it is! Most gardens have a top layer of soil and is given the name "topsoil."
Usually that soil is pretty easy to dig up and for most people it will be classed as fertile soil. In other words you will be able to grow plants in it. In most cases this topsoil is usually about the depth of the head of a spade.
Now picture a garden where you have removed the topsoil. The layer of soil left is known as a subsoil and will almost always be more compact. Some gardeners refer to this as a "pan." Digging that soil helps break up that soil and allows air to start flowing through it. If you can also add humus or compost to that subsoil, then that can help a lot with fertility and really help the soil to drain a great deal quicker.
This can be back breaking work, though for bigger areas you can hire something like a cultivator to do the hard digging. You can also enlist a few friends.
Best Method for Double Digging
- If you do plan on doing this by yourself, then we recommend doing it in strips of about 2 feet wide.
- Measure out a strip of ground about 2 feet wide
- Remove the topsoil to about a depth of 10 inches (25cm) and put it to one side
- Then dig down another 10" and add some manure or well rotted compost using a garden fork
- Mark out another strip of 2 feet and use the topsoil from that to fill out your first trench
- Then dig your second trench with your fork and add some manure or well rotted compost
- Keep repeating this until your ground has been completed.
- The initial topsoil you removed can now be used to fill in the final trench
We have mentioned using rubble or old tiles for drainage. Opinion is divided on this as to how effective it really is. Our opinion is that for most gardeners who suffer from flooding or wet soil, the best thing to try first is double digging. That will work really well for a lot of gardens.
If however you try that and it doesn't work to your satisfaction then we do think it is worth creating a few trenches. You don't need to be too technical about making these.
In large areas such as farms, or for large lawns, French drains do work well, but they are not really a practical solution for most home owners. With a French drain, you dig a slope by digging a trench at a 1 degree gradient. You make this trench wide enough to hold a corrugated pipe.
The pipes come in 60 to 200mm diameter sizes. (2.5" to 8") and the size of the pipe that you use depends on how much surface water you have.
The trench is then covered with a water-permeable landscape fabric. You put enough fabric under the pipe, up the sides and enough to fold over the pipe.
Fill the trench with a landscaping aggregate to fill the bottom of the trench to around a third. The size of the aggregate that’s should be between 1 to 2cm. Lay your chosen drain pipe with the perforated holes face down.
Put in more aggregate on top of the pipe in the trench until it is about 10cm from the top of the trench. Wrap the fabric around the aggregate. We have summarised these steps below:
- Dig a trench
- Cover it with a landscape fabric
- Fill the bottom of the trench with a landscaping aggregate
- Lay the pipe with the holes facing down
- Add more aggregate
- Wrap the fabric around the aggregate.
- Cover with a layer of soil
So as you can see there are a number of methods available on improving soil drainage. If you plan on doing any of these yourself, then just be aware that they take time and you do have to be patient and see if they work. The good news is that once you fix the problem, then it is permanently fixed.