How to Install a Garden Drainage System (and When)

Last update: 2 months ago

10 min read

waterlogged garden

Water is the source of all life, but too much water can cause significant problems even in the garden space. For instance, surplus water can promote root rot and diseases amongst plants.

If your green space turns into a poodle-land every time it rains, this may indicate that your garden is in dire need of a drainage system. Below, you will learn what a waterlogged garden looks like and how to find out if yours is retaining too much water. You will also discover how to improve the drainage in your garden both organically and through feats of engineering.

What Is a Waterlogged Garden and What Causes It?

Signs that you have a waterlogged garden

It’s very likely that you will recognise a soggy garden when you see one. Some of the symptoms include multiple puddles caused by rain that have trouble draining, squelching sounds upon stepping on the soil, reed or similar plants growing in the lawn, and the presence of moss.

10 factors that can lead to poor drainage

While there are myriad of reasons why your garden isn’t draining water properly, here are 10 factors that most likely contributed to your garden’s swamp-like appearance:

  1. Underground springs changed their direction as a result of heavy and continuous rainfall.
  2. Subsoil and topsoil were mixed together during property construction, creating compacted soil that water has a hard time draining through.
  3. Your property and garden have been built on top of a water-retentive clay layer (a pretty common situation in the UK).
  4. The garden is situated at the bottom of a hill or lower than those of your neighbours.
  5. You or your neighbours have built swimming pools, home extensions, or any other structure with a foundation deep enough to divert water.
  6. Your lawn or garden has an uneven surface that allows excess water to form puddles.
  7. Your garden or yard features a driveway, patio, or other impermeable surfaces.
  8. The guttering of your house is blocked or not connected to a drainage system.
  9. The level of the natural groundwater under the soil (the water table) is too high.
  10. Your neighbour’s garden drainage system diverts water to your property.

How to Check If Your Garden Has a H2O Problem

Most drainage projects are not cheap. Before looking into any garden drainage ideas, we highly encourage you to confirm that your green space indeed has trouble draining water. Here is how:

  • Dig a hole into the soil that is approximately 60cm deep;
  • Fill the hole with water and leave it be for about four hours;
  • If the hole isn’t empty upon your return, then drainage is needed.

Note that, sometimes, especially after a heavy rain, accumulated surface water may also not drain as fast as usual. This, however, could mean that your soil simply needs to be aerated.

Types of Garden Drainage Systems

Before doing any digging work whatsoever, always think about where the water needs to go first. This means that you need to locate a ditch, stream, or a soakaway (more on these later) that is located in close proximity to your garden in order to redirect surplus garden water there.

In some parts of England, connecting a drainage system to sewers or storm drains is forbidden, so always make sure to consult your local authorities first to avoid a fine. It should also be noted that drainage work has to be done from late summer to early winter when the soil is usually dry.

Simple ditches

To create these, find a slope and dig the ditches (about 90cm deep) with the help of pedestrian-controlled trenching equipment. Note that the ditches should feature sloping sides and should be dug out at the lower end of the slope. Although basic, this type of drainage system will usually do the trick and will divert extra surface water away from your garden.

French ditches

french ditch This sloped ditch is perfect for redirecting stagnant water to a drain. Most trenches of this type are usually around 15cm wide and 30cm deep. To create one for your garden:

  1. Find a slope and dig a horizontal trench across its length in the direction of the drain.
  2. Use a string and a string level to adjust the slope of the trench and check it constantly.
  3. Before using gravel, line the trench with landscape fabric for improved water percolation.
  4. Use a shovel to fill the bottom of the trenches with gravel and fold the fabric over it.
  5. Add gravel on top of the fabric and make sure to spread it evenly to preserve the slope.
  6. Cover the ditch by evenly distributing topsoil across its entire length.

Herringbone drainage

herringbone drain pipesJust like a French ditch, the herringbone drainage is built on a slope. However, unlike the French ditch, it consists of several trenches that are connected to the main drain, thus forming the so called herringbone pattern. This technique is best used on flooded lawns or gardens that are irregular in shape. Here is what you need to do to install a successful herringbone drainage:

  1. Mark the position of the main trench. It should begin from the highest part of your lawn or garden and end at the lowest.
  2. Mark the position of the side trenches and ensure that they join the main drain at a 45 degree angle to form the herringbone pattern.
  3. Space out the side drains at either 3 metre intervals (for clay soil) or at 7.6 metre intervals (for loamy soil);
  4. Line the trenches with landscape fabric to improve water percolation.
  5. Use a shovel to fill the bottom of the trenches with gravel and fold the fabric over it.
  6. Add topsoil to the trench and dig a 1,2 metres-deep soakaway (a pit filled with hard core where water slowly soaks into the soil) at the lowest end of the main trench.
  7. Link the main drain to the centre of the soakaway hole.

Piped drainage

piped drainageJust as with the previous methods, this one also involves digging out sloped trenches, lining them with landscape fabric, and filling them with gravel and topsoil. But here, you will also need to purchase and install perforated plastic ot corrugated land drain pipes inside the ditches.

Why would you want pipes with holes in them when you can go with a regular non-perforated one? If you have only one spot where water forms a puddle after rainfall, then this method is probably is not for you. If your soil is uneven and you have several spots, then perforated drainage is the way to go.

Because the pipes are perforated, water will get inside from every angle and not just from the lowest part of your garden. That way it will be more easily distributed. Important to remember: the holes need to point down. Otherwise the water would need to fill the entire ditch before it has a chance to reach the holes. The photo is just an example to illustrate this type of drainage and should not be followed without initial preparations and research.

Designing and installing piped drainage systems is a monumental task and should only be handled by certified landscapers.

Other Ways to Fix a Soggy Garden

Pick the right plants

One of the easiest and cheapest garden drainage solutions is to plant vegetation that is compatible with your soil type. For instance, some hydrangea species are great for regulating wet soils, while clay soil gardens will benefit from species like Geranium and Fuchsia.

Get yourself a rain barrel

Sure, your house may have a guttering system in place, but does your shed or greenhouse have one? The good news is that installing guttering on outbuildings is a relatively simple task. Once the gutters are affixed, redirect the downpipes to overflow barrels. This way, not only will you avoid flooding your garden, but also have an extra water supply to use during dryer months!

Cultivate a grassy swale

If you have extra space in your garden, try growing a “grassy swale” (also referred to as a “contour bund”). Such lush sections should be grown on a gradual slope. This will ensure that excess water will be able to run off and drain away at that location, keeping your garden safe.

Enrich the soil with organic matter

As silly as it may sound, this neat trick actually works. All you need to do is add copious amounts of organic matter to your soil. This way, the soil will absorb all needed water and will allow excess moisture to pass unhindered.

Create a bog garden

If nothing else helps and water keeps emerging from the ground despite your efforts, you can always opt for a rain or a bog garden aesthetic. This means planting water-loving plants, such as maple, fern, mint, irises, and other species that will have no trouble getting their roots wet.

DIY Drainage Methods That Will NOT Work

With the wealth of knowledge that is available on the Internet today, it’s all too easy to pick a garden drainage method that will not work at best, and ruin your garden at worst. Take a look at some of the more popular offenders out there and try to avoid them at all cost.

  • Replacing the top 12cm of clay soil with loam soil. The only thing you can achieve with this method is to temporary conceal your water logging problem. However, be sure that your cosmetic fix-up will turn into a spongy and icky mess at the first sight of rain.
  • Digging soakaways for clay soil drainage. Don’t try this under any circumstances! Digging a soakaway into clay soil will cause the hole to overflow and will lead to a flood!
  • Planting trees or shrubs in a waterlogged garden spot. Not only will the plants fail to drain the water, but they will also perish since their roots will need to breathe. Your only option here is to plant bog plants, but they won’t be able to solve your problem completely, either. Instead, you will essentially create a different type of garden.
  • Adding topsoil without creating a hardcore or gravel base first. By adding nothing but topsoil on top of already spongy soil, you will only exacerbate the problem or, best case scenario, shift the mini-flood from your garden to that of your neighbour. Not good.
  • Elevating the whole garden via raised beds or with an additional layer of gravel and topsoil. This MAY work but, since the water won’t be going anywhere, you yet again risk shifting the problem to another area as with the topsoil method above.

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So, there we have it, you now have all the information you need to deal with a waterlogged garden. Do you have any extra tips that you would like to see included? If so, leave us a response in the comment section below, and follow us on social media to ensure that you won’t miss out on any future garden landscaping and maintenance tips & tricks.

You can also contact us at any time of the day and night to arrange a landscaping session. Until next time and happy gardening!

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9 CommentsLeave a comment

  • Drainage issues come up here in California too. I can imagine with all the inclement weather in the UK this is a serious issue for lots of gardeners so glad to see a post addressing it.

    • Thanks a lot, Rich! Indeed, it’s a big issue around here and hopefully, our post helps throw some light on the matter.

  • We’ve had extensive subsoil issues on our property and consistent floods, so I know the pain of a drainage system not working as it should.

    • Hello Sebastian,

      Yes, we support the Hampstead area as well. If you are interested in arranging a landscaping survey, you can contact us here, or call us on 020 3404 2272.

      Happy gardening!

  • Hi – I am looking to put in a couple of soakaways to stop my garden flooding. I know it needs to be 5m from the house but my neighbour is insisting on 2.5m from boundary and 2m deep – I can’t see this anywhere and being told this is not the case. Can you advise

    • Hello John,

      The following resource might be of use for you. In brief, it says that a soakaway should be built both within 5 metre of a building or a road, as well as 2.5 metres away from a boundary. You might also want to check in the other relevant documents mentioned in this article.

  • Hi Fantastic Gardeners,

    I read your blog on drainage solutions and found it an excellent read. Easy to understand and act upon. We recently had a garden that was very slipped at the back. We and our neighbours wanted to get the gardens in the back level so the kids could play out the back so we decided to backfill it. We placed boulders at the end of the garden and backfilled with a mix of sand and topsoil. Parts were soggy and I thought we would need to dig it all up and place pipping to drain. That is until I read your article. Upon reading the article we planted hedging around the edge of the garden and we watched it soak up the excess water and it solved our problem. We done this at very little cost and would never have thought if this as a solution until I had read your blog so many thanks I would highly recommend it.

    Regards
    Chris

  • Awesome post. I have just been looking at sorting drainage in my garden so this will be a huge help. Thanks!

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