What's the best way to improve heavy clay soil

PhotiniaPrincess · February 2021

Hi all, I'm on a new build estate and our garden was just very heavy clay soil when we moved in. I'm trying to improve the drainage before we start landscaping. What is the best way to do this? I don't want to plant in it as we intend to pave the majority of it and just use pots. Thanks in advance.

robairdmacraignil · February 2021

Organic matter is very important to clay soils being able to clump together and form aggregates or peds that allow air and water movement through the soil. Compressing the clay when it is wet should be avoided. Root action of plants that are tolerant of damp soil will also help the soil structure in the long term but adding an organic mulch to the surface will help encourage earth worms and other soil life to move in the soil and give it better structure as well. My own parents back garden was damp clay and I planted lots of fruit shrubs and trees with black currants doing particularly well and also collected large volumes of used horse bedding I got for free to the surface and it is much better draining now. Wood chips in the horse bedding in particular last for a good while and helped but if you are paving areas then a different approach with hard core stone and coarse gravel might be needed. My parents' back garden was so waterlogged I had to put in a few drains initially to help it dry out and allow the fruit trees and shrubs a better environment to get established.

purplerallim · February 2021

As you are just in do you know if it has a slope? That would be the first question and has it flooded?

owd potter · February 2021

Clay soils are very reactive to moisture content.
When wet they swell, when dry they shrink.
This manifests itself in possible movement of the surface and whatever you lay over it, especially if vehicular access will be required.
Everyone knows of an uneven driveway somewhere...
So the soil drainage question is really consequent on what use and how you intend to pave, as will be the paving construction too.

Loxley · February 2021

When you lay your paving the water will run downhill, so at that point you will need a drain to carry the water away. On a free draining soil you could use a soakaway or just drain into a planting bed, but that won't work on clay - although you could have a sort of 'rain garden' with plants that cope with periodic standing water.

As Owdpotter says, the sub-base for the paving will need to account for the shrinkability of the soil.

PhotiniaPrincess · February 2021

Thanks everyone, that's helpful. It does have a slight slope that runs towards the house and I've already put a channel drain in before the patio. I've put 6 land drains in (although I'm thinking of adding 2 more next year) and I've turfed it for now so that it's a usable space. I plan to level it and pave it at some point in the future. Would adding chicken manure pellets to the lawn after cutting help improve the drainage at this point? I've already got manure and bark around the edges.

Loxley · February 2021

Chicken manure pellets won't do anything. Does the patio slope away from the house, with the channel drain at the point where it meets the grass?

If you pave the garden, that is where you want your drain (with a fall across the patio). I presume it's connected to the house drains? Sometimes you see them not actually connected to anything!

PhotiniaPrincess · February 2021

The slope runs towards the house and there's a channel drain now in between the grass and the patio which sits in front of the house. Just wondered if there was something I could be treating the soil & grass too in the interim that would help improve the texture of the soil before we landscape it.

purplerallim · February 2021

It's more a case of stabilising the substrate onto which you lay paving than improving the soil for planting in your case. As for paving a good foundation of sand and not fixed with concrete would be better, as when you get movement, which you will, its easier to lift and re set individual slabs than chip out concrete to re set.

Loxley · February 2021

There's not much value in improving the soil if you are planning to pave over most of it anyway.

Inglezinho · February 2021

Don't. I badly injured my back trying to improve clay soil. There are many plants that are very fond of clay and you will never have a drought problem. If you insist, dig in sand, grit and compost when planting, spread an organic mulch on the surface round about now, but please please avoid a lot of digging. Clay soil is where you are at. A better and safer way of using your time to get a soil analysis done to see whether it is acid or alkaline, this will give you a much better idea as to which plants to choose. Good luck!

What's the best way to improve heavy clay soil

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