300mm of topsoil –> over a metre of compacted clay!!

Hi
New build back garden has no drainage whatsoever!
Lawn has been laid onto approx 300mm of topsoil but beneath is a large compacted layer of dense clay! I have dug a few test holes and it goes down over 1.2M (I couldnt dig any further with a post hole digger)
So now I dont know what to do?

Hire someone to remove it all!
Lay French drains(very deep)!
Put in some Acco drains around the edge?
Remove just the topsoil and work in some gypsum and manure and compost?

I have David Austin roses that are drowning amongst other plants that dont swim well!

Any help or experience would be greatly apreciated
Thanks
John

 

Removing that amount of clay will be expensive, then you will have to replace it with something more suitable or have a sunken garden that your neighbours gardens will drain into.
Acco drains appear to be surface drains and I suspect won't make much difference to how wet the soil gets.
I think I would go with French drains, the question then is where does the water from them go to; a soak away, an existing drain or watercourse?
Another possibility would be to have raised beds for the plants.
Also where is your property as the best option may be different in dryer/wetter climates.
I'm sure there will be other suggestions coming along soon.

 

Hi @John Bradley - sadly this is a common occurrence with new builds, and yours sounds like one of the worst.
I think you'd have to go down the drain route. Not something I've ever had to do, fortunately, but others should be able to help.
The problem with trying to carry on with it as it is, is the eventual lack of drainage low down. All plants need drainage unless they're pond plants - even bog plants need some, and it isn't easy to establish anything, as you've found.
The only other option is to go 'up'. Raised beds for plants. That's what I do. As to the grass, you can do that for it as well, but it depends on the size of the plot. It also depends on your general climate as to how well it will do. I made a raised lawn here, because there was no garden - it was all paving slabs and gravel, over compacted clay. I left a lot of gravel in the mix too, to counteract our rainfall here. Grass only needs a few inches of soil to grow, but if you're in a wetter part of the country, you may find it'll get very messy if you use it frequently - kids, pets etc. That's where the size of plot is a factor - it's easier in a large area becuase the load/footfall gets spread.

 

Since it's new build, is there any way you could get the builders to do something? Also, if it's part of an estate, I'd have a wander and find out if any neighbours have the same problem - if you put in a group complaint it might work better.
Do the test holes fill up when it rains? That might imply there is SOME transverse movement of water. The problem with french drains is that if the clay is really impervious, you'd have to have them pretty close together.

 

Are you actually experiencing any issues with drainage?

We used to have a garden with heavy clay and never had any issues. Nightmare to dig into and work with but otherwise great for growing as clay soil is full of nutrients. Adding home-made compost gradually improved the soil.

 

I agree, you need to find out if its just a fairly local problem in just one or two gardens or a general problem.
Could be as simple, (not simple in reality), of just breaking up the clay underneath.
This seems to be a major problem with all new builds, are they building on swamps or is it a case that the natural drainage for the area has been cut off in the building process.

 

Lucky you! Clay soil to grow your roses in, they love getting their feet into the stuff. Also brassicas if you are into growing veg.
Raised beds seems to be a good solution, also cheaper and easier on the back than laying drains, getting someone in to remove it etc.
I inherited a clay garden at my last house. I dug in lots of grit and manure, it took a few years but ended up friable, nutritious and a get garden.

 

One big factor is the use of JCBs and the like. If anything's going to compact subsoil, it's the use of heavy machinery.

 

Thank you all for your help, we live in Shropshire and there are several houses with the same issue, sadly the builders arent accepting any liability for the drainage problems!
So its down to individual time and cost

The issue we have is the patio area floods and the lawn is just sodden all through winter! We only moved in last June so this will be our second winter?
I think I might just put in Acco drains around the patio and try French drains in the lawn to see if that helps?
I think raised beds for my roses is the only way forward as taking out that much clay would be too time consuming and costly! Thank you all again for your help

 

I agree, but only up to a point, the clay subsoil in my garden has probably not been disturbed for 80yr, so it must be pretty well packed down.
I tend to think there are other things going on, but I'm not clever enough to work it out.
Having a flat area upon which you just spread top soil is a bit unnatural imo, you tend to create a kind of sponge on top, that acts like a jelly.

Drains are OK, but you might end up draining the entire neighbourhood and where is the water going to go.

 

Drains definitely need careful planning, as I found out Unless the plot is on a slope, you also need to allow a fall in the pipework. And never underestimate how much water will eventually exit wherever the drain stops!

 

Thanks, the garden is only 6m2
And it slopes towards the house so I will have to get a mini digger in to create a very deep soakaway!
Thank you for the help though its much appreciated

 

That's not good - they have left you with quite a problem. I'm not sure acco drains would be enough particularly as the lawn slopes to the patio- and would you have somewhere to direct the outflow? Maybe a french drain along the edge of the patio, draining into a sump full of big stones, and stand a nice pot on it.

 

Yes they have! I think I might go with French drain and dump it all into a soakaway thats the only way I can see to sort it?
Thanks for the help though

 

Builders will never acknowledge there's any problem, let alone come back and fix it. You have to sort these things yourself. It's a dreadful problem in all areas of the country with new builds.
Sometimes you can just have one or two small areas, but when anything's being built, it's natural for ground to be really compacted, and when it's clay, it isn't simple to fix, because of the nature of it.
There was no chance I was going to mess about and wait for organic matter to do any good here in this plot when I moved in. The bit which had been grass was easier, but even then, I made an edging for a new border and added loads of manure which I had a source for as I worked in a stable. It was then easier to plant into 6 months later, but it's ok if you have your own material to add to it regularly, and it's also easier for shrubs and trees rather than flimsier planting, or anything that needs sharp drainage. When I've had to dig down to improve odd bits, it was hellish to deal with, and when I built a bigger pond, it was dreadful because of the underlying ground. I had previous experience of it so knew what to expect, but if you're at the end of a row of properties, you also find all the rubbish/rubble when you dig, because they just dump it.

With heavy clay, if you dig a hole - the amount you take out looks like it would fill a container twice the size, so I'd say save yourself a lot of grief for your roses, and any other plants, and go upwards, and make the beds a decent height. It can be expensive initially, especially filling it, but it saves a lot of pain - in many ways!