2

My lawn turns into mud between October and April every year (UK), and then in the summer becomes almost impervious to garden forks. If I do manage to break the surface, it's still fairly damp underneath. The topsoil varies across the garden but is mostly medium to heavy clay, with some more sandy areas and the odd lump of chalk. In winter, it generally remains muddy even after a week or two without rain. It doesn't rain that much here, but it's damp, dark, and drizzly all winter. My goal is to have a garden where I can let my dog out in winter without him traipsing large quantities of mud back into the house.

To see if a soakaway/dry well is an option, I dug a test hole a metre deep and filled it with some water to see if it drains. However, after three days, the water level had not dropped noticeably, suggesting that my subsoil is mostly impermeable. However, in my area, I am allowed to drain the lawn into the storm drains, so that should not be an issue.

I read a lot of reputable sources suggesting online to install a French drain system, by digging trenches of ~45cm deep on a 1:100 fall, with perforated pipe and gravel wrapped in non-woven geo-tex, spaced ~3 metres apart, then covering them with fresh topsoil. To test whether this might work, I excavated some trenches in the muddiest part of the garden, then turned the hose on a metre away to see if the water flows through the soil and into the trench. However, that did not happen - instead, it just formed more mud where the hose was running and the bottom of the trench remained empty and dry.

So now I'm wondering: will a French drain system will even work if I don't fix my topsoil's permeability? What good is a drainage trench if the water can't even percolate through the heavy topsoil to get to it?

My options include:

  1. Continue digging trenches for French drains and trust that over time, everything will work and the garden will magically become less muddy.
  2. Install the French drains as above, but also excavate and remove all of the topsoil, grade the clay subsoil so that it directs water to the drains, then replace the topsoil with newly purchased loam.
  3. Install the French drains as above, but fix the existing topsoil's permeability by rotovating in large quantities of sharp sand, grit, well-rotted manure, and bark.
  4. Don't even bother with the French drains, just fix my topsoil as above, either by replacing or rotovating with grit and organic matter.

I'm leaning towards 2 or 3, but before doing anything too drastic it would be nice to know if I'm being sensible. For reference, I had a few landscapers around, and they mostly tried to pressure me into artificial grass because the soil here is apparently a nightmare. The best quote I had for fixing the situation and installing a real lawn was £20k (the garden is 20m by 8m), and that involved removing all the topsoil down to a depth of 30cm, adding a layer of gravel and sharp sand, then a new layer of topsoil. That didn't sound like it would fix the underlying problem to me, just delay it, but he said it's worked well for other clients several years on.

Edit: The compaction is caused just by walking on the lawn when it's muddy e.g. to get to the shed or rabbit hutch, but I will be putting a gravel path down instead. Plot is around 130 years old, but the house got hit by a rocket in the war, and the garden contains a lot of the debris from the original house (occasionally UXO is found in nearby gardens when landscaping). I'm not sure if the debris causes any problems, but having walls buried under the soil probably isn't helping.

Sunlight is full sun over summer, but when the sun gets low in the sky over winter, it rarely gets direct sunlight (if it's ever not cloudy anyway).

1
  • Cost .vs. speed. 2 will cost the most, and be fastest. Other options will cost less and be slower. It's a tradeoff. Have you aerated this disaster of a lawn? Do you have a soils test result?
    – Ecnerwal
    Nov 28, 2022 at 18:30

1 Answer 1

2

You're right in thinking that if the water cannot percolate even down a couple of inches, then it won't percolate into a French drain. Given that your perk test results were so horrendous, I hope you're on a municipal sewer rather than a septic system.

At this point, I'd talk with a landscape architect who is unaffiliated with a landscaping company, not a "landscaper" who has a vested interest in getting as much money out of you as possible with the least amount of time spent. Talk about French drains, regrading, soil compaction, the perk test that you did, possible impacts of using heavy equipment on your lawn when it's so wet, etc. You will have to pay a consultation fee, but IMO it's money well spent for peace of mind that you're doing the right thing.

There is an Option 5, though: Pave an area for the dog to run on and fence it from the mudpit... err, rest of the lawn. This may be your cheapest option.

If you don't want to/aren't able to talk with a landscape architect and if Option 5 isn't possible, then I like Option 2A - Option 2, but without the French drains and with improved grading to an area away from your yard (and your neighbors' yards). Lay the new topsoil directly on top of the subsoil - adding gravel/sharp sand between loam and subsoil will either do nothing except make your wallet lighter or make the drainage worse due to its creating a perched water table (water will percolate to the gravel and then rise to the top of the loam - making it both muddy AND quicksandy).

Question - if you replace the "topclay", how will you know if they give you loam or if they just dump more clay on top of the subsoil and a couple inches of loam at the top?

Right now, your clay and subsoil are both extremely compacted, and using heavy equipment to scrape off the clay with the soil so wet will make the subsoil potentially even worse. If possible, you should wait until the soil dries out some, which sounds like next summer. At that point, after they scrape the clay off they should use deep-tine aeration on the subsoil to break up compaction. AND THEN IF THE SUBSOIL IS NOT COMPLETELY DRY, NO MORE HEAVY EQUIPMENT. This means that the loam is added to the site view wheelbarrow. I know that contractors love their toys and think that heavy equipment is necessary, but in your case, running what we in the US call a skidsteer over new loam, especially if wet, will just compact the heck out of it and make the drainage bad again.

1
  • Not a bad suggestion for the dog, and a little wall and fence separating the patio could be a nice feature too.
    – Cameron
    Nov 29, 2022 at 1:28

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.