Clay

susanpercival12cGxX9sL · May 2022

Hi everyone
My husband and moved into a new build in Dec 2020 (the wettest winter for a long time) and the land is known for flooding, and I now understand why - the builder lay 10cm of top soil over solid blue clay. I’m talking wet, sticky potter’s clay.

The builder put a land drain down one side which hasn’t done anything at all as the landscapers dug out all that clay and lay it all back over the top of it, effectively waterproofing it, despite my protestations. We have spent the last year fixing the south-facing bed which has involved a lot of compost but seems to be breaking up ok because it dries out. The same can’t be said for the east facing and and north facing areas, which have standing water even after a month of no rain. I’ve lost too many plants to count as they have rotted away. Digging into the ground makes a suction sound and it smelt awful. Not a worm to be seen despite me digging in organic matter - the water simply has nowhere to go.

My husband and I have over the last month bit the bullet and dug out by hand to between 2 and 4 feet to a level where the clay seems drier and easier to slice out, like hard cheese rather than ripping it out like soft butter.

We have filled 2 midi skips and 2 builders skips.

When we started the work, over the course of 2 weeks one small area where we had tried to go even deeper (5 feet) but gave up when we realised it wasn’t going to get any better - the area is naturally at the bottom of the land as it slopes west to east and north to south - filled up with water from the surrounding soil, despite no rain. We ended up at c15 large gorilla buckets worth of water but no more has appeared since.

So after all that background here is where I would be grateful for your help:
1. Am I correct in thinking that the water that leached out was trapped/standing and the surface area should now start to dry out?

2. If we now refill the area with decent top soil, and plant out, knowing that there is solid clay at the bottom, will it eventually fill up with water? Or will the plants and warmth stop it ever getting that bad?

My concern is we have only delayed the issue and not fixed it although I’d like to hope that an awful lot of water would have to fall to fill the area.
Hope someone out there has been through the same.
Susie

Fairygirl · May 2022

Organic matter is the key to improving clay. If you add soil, it may not really work unless it's to a considerable depth, and that could be prohibitive.

New builds are notorious for rubbish soil - and compaction is a big problem with clay, hence the problem you have. When the compaction comes over that type of soil, it's even worse.
The other alternative is to make raised beds to plant into. I find that much easier

Cecelia-L · May 2022

I had a similar issue when I first move to this house. I tried everything but resorted to installing hundreds of meters of land drains leading to a looooong ditch designed to hold all the surface water so that the land will be less boggy. Plus a soak away with a pump inside that pumps the water into the land drain if it gets too bad.

Water always go to the lowest point with the weakest pressure. Unless you guide the surface water elsewhere the newly dug area will become a soak away and all the plants will rot over winter.

Actually building a soak away is a good idea, or a pond, or some type of reservoir to hold all the excess water to allow the clay to have a chance to be mended into workable soil.

Raised bed is another option, which is what I have gone for even with all the land drains and ditches and soak away and pumps.

All the best of luck 🤞

MikeOxgreen · May 2022

You need to post up some detailed labelled pics and maybe even a drawing for anyone to even begin to get their head around this.
Can the land be drained down to a lower point or are you at that low point?
It sounds to me like you need to get a land drainage expert in if you want it dry, but another way is to put plants and trees in which like clay.

punkdoc · May 2022

If it really is green, you should probably seek medical attention.

Fairygirl · May 2022

Have you got some photos @susanpercival12cGxX9sL? I should have asked that yesterday. It would give us and idea of the scale of the problem.

I don't think constantly trying to dig it all out will be the solution. Fine for a small area, but if it's large, you're going to be sick to death of it very quickly, and it's soul destroying.
Drains only work if they're extensive, and then you still have the expensive problem of replacing soil and trying to create a garden. It also depends on what kind of garden you're trying to achieve

Chris-P-Bacon · May 2022

Post a photo.
It smells because it's most likely more a silt than a clay. Your garden was probably a naturally occurring pond in a previous life.
Installing land drainage is expensive ...and messy...and still may not work how you'd like it to. If you have the budget - go for it. I probably wouldn't.
Raised beds work - I garden in almost exactly the same conditions as you. Where I haven't used raised beds I've added organic matter which will also work but I started over 6 years ago and added literally tons to a relatively small garden. It's a long term fix.
Soakaways in a clay soil don't tend to be worth the effort in my experience.
In the end I planted mainly bog garden plants - Rodgersia, Marsh Marigolds, Purple Loosesrife, Persicaria, Cornus etc which did great.
Planting a tree is also a good idea. River Birch or Alder spring to mind...but you'll need lots a room..and don't plant near buildings!
Don't get stressed...you have lots of options.

AnniD · May 2022

I think building up (that is, raised beds), will be much easier than digging down, to put it mildly.
As others have said, if you could post a couple of photos, together with the sort of planting and look you're trying to achieve, that would be a great help

raisingirl · May 2022

You can make a sump so the water pools in one area and the rest is dryer but there's probably no point making a soakaway - there has to be somewhere for the water to go for a soakaway to, well, soak away. If the ground is waterlogged, the soakaway just fills up. You can't connect a drain to the sewers (it's illegal in most parts of the UK). Trees and woody shrubs will break up the subsoil and also take up vast quantities of water when they're in leaf, so your garden would be much dryer in summer but potentially waterlogged in winter.

Monty Don's garden floods every winter for a few weeks. It's not a catastrophe - you need to research plants that will cope with being flooded in winter and design your garden to work with that (i.e. don't put a lawn or patio at the bottom end, create raised beds for all but the summer planting, don't plant trees that die if they get waterlogged for a few weeks.)

Work with your conditions - it could be lovely

susanpercival12cGxX9sL · May 2022

We have already dug out, c7 tonnes I think, here are some photos. Whilst they don’t appear to be, the walls and floors are solid clay, they’re just covered in cave-in soil from the top. As a few have mentioned it isn’t ever going to soak away.

I plan to plant a small, slow-growing tree or tall shrub in the smaller curved area (it would be 1.8m away from the house), along with plenty of plants. The larger area will be both planted and gravelled with moonstone, with some stepping slabs inbetween.

I plan to fill the entire area completely with soil as it’s more absorbent than gravel; I’m hoping that the plants will take up most of the water and the sun will do the rest; it’s just if we have a really wet summer or winter there’s nowhere for the water to go.

I appreciate a lot of peoples’ gardens flood when it’s really wet but the water probably does drain, just really slowly. Here, it’s solid clay with no breaks so the water really doesn’t have anywhere to go, my case in point being when we started to dig out, the deepest hole filled up with water every day for 2 weeks when it hadn’t rained for 4. The main culprit was what’s left of what was the curved bed containing the water bowl. There was around 15 large gorilla buckets worth of water. The water that filled in that area had likely been standing since Winter 2020. When I dig fresh holes in the bed halfway up, water springs up. I think it’s because there is so much clay on the entire site the water just sits until it gets an opportunity to escape. That doesn’t happen in the South-facing area but that could also be because it’s at the top of the slope so the water is running downwards. No more water’s accumulated since we got rid of the main batch so we really are hoping we have drained it all down; the worry is it coming back!

Fairygirl · May 2022

I don't think that looks too bad at all

If you backfill with loads of manure, and maybe a few bags of pea gravel, plus the soil you took, [or new stuff if you've already got that] all mixed together, it should be fine for adding shrubs/trees according to what you prefer. A mix which improves the general soil structure will aid drainage, but also help prevent cracking and serious dryong out if you have a lot fo dry weather through summer.
The more plants you have, the more the moisture will be taken up. Plants which like moist soil will be happy - Acteas, Ligularias, Camassias etc.
Acteas are good in shade, but with enough moisture, they can cope with quite a bit of sun. Likewise Camassias.
The fact that you have what looks like a Geum growing nearby, plus Acers, and a lawn, suggests it isn't as horrific as it seems. Acers don't like wet feet on a permanent basis, even though they like loads of moisture

Clay

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