Heavy dense clay

[SWOTHEAD]

I terraced a section of my garden which involved digging out heavy clay from a sloping bank. The result is a flat, raised area about 50M2, where i would like to sow grass seed and dig out the ground for 5 pixie size fruit trees.
Problem: water will not drain and lies in puddles. i considered laying a French drain, but the clay is so dense water will not percolate into the perforated pipe. When I ram a steel bar into the clay about 24 inches, i reach a base of rubble and the water drains, but only where the hole has been driven.
When the clay dries out it sets like concrete.
I can't see that digging a sump/soak away would work, for the same reason.

Amending the clay by digging in organic material/sand etc would be an enormous job and might not work.

Question: would laying say 3 inches of 50mm stone chipping and then cover with say 3 inches of good soil do the trick? Would the water drain away if i create a slight slope, or will it just accumulate and as the water table rises kill the grass and trees (eventually)?

Of course i could just gravel the whole thing, but that is not what we would like

Any suggestions?
Thanks!

 

[DirtMechanic]

So here we have the heavy clay and it is a 5 PH due to lots of rain leaching out any materials that act as liming agents. Many clays are the opposite, in that they do not leach like ours and are alkaline. Which are you interested in? The reason I ask is that the very thing you are mentioning with a layer of rock is used around here as a trick for plants that like a more neutral soil. Layers of marble stone chips act as a long time alkaline barrier into which we can put neutral soils which some plants like say a clematis would enjoy more. You would have the same opportunity if you were to build a soil horizon back upon that clay. You could also pitch the earth for drainage as a driveway or road is built. I would encourge you to do this no matter which path you take as clay can easily drown some plants unless it can drain to some degree.

 

[Marck]

Greetings, welcome to the Forums.

I found the other thread with the photo, so I'm returning to this thread to add to my response.

After seeing the photo, I will add that the situation is not hopeless. amending and mounding could turn such soil into a fine garden, at least for clay-tolerant species.

Of course, you want a lawn, so do amend generously before planting (yes, it will work) and then plant a grass species that is adapted to seasonally wet clay. Turf cultivars of Tall Fescue (Festuca arundinacea cvs.) might be a good option. Some say it makes a coarse lawn, but really it can look very good. It's a lawn, not a putting green.

If it is true that across the entire terrace, there is a 'base of rubble' that drains, you could do something with that.
Perhaps, dig a number of two-foot deep holes. one or two feet wide and fill them with a mix of gravel and compost.
Perhaps ten holes or so, depend how the 50 square meters are arranged.

Always consider plant selection. Plant species (grass or otherwise) that prefer heavy, seasonally wet soils.

 

[Sheal]

Grass needs a minimum of 4 inches of soil to grow reasonably well.

 

[DirtMechanic]

Grass needs a minimum of 4 inches of soil to grow reasonably well.

So 6 or 8 inches of loose compost and wait a year?

 

[Marck]

The description of the clay in the OP is not that different form the soil (clay is soil) found in the grasslands of California, as well as being the base soil of my garden. Unamended, it is heavy muck when it rains and concrete-like adobe when it dries. All the same, with water, the grass and many other plants grows lushly.
By all means increase the organic matter by amending with compost, but no need to wait a year. Seed or sod can be laid down immediately after. Plant selection is key.

 

[Sheal]

So 6 or 8 inches of loose compost and wait a year?

Sorry @DirtMechanic I don't understand your reply.

 

[DirtMechanic]

Sorry @DirtMechanic I don't understand your reply.

When I put out 6 to 8 inches of compost it takes a long time but it will melt down into a 2-3 inch layer across a year.

 

[Sheal]

I'm with you now. But knowing that compost rots whereas soil/dirt doesn't it will eventually disappear.

 

[DirtMechanic]

I'm with you now. But knowing that compost rots whereas soil/dirt doesn't it will eventually disappear.

Yeah. So in honor of that fun fact I loaded 8 wheelbarrows of charcoals into the garden. Its the only slow to leave version of carbon I know of to help slow that return to suffocating, acidic clay.

 

[Sheal]

It will certainly help the situation. I have sandy loam which drains very quickly and it's impossible to keep it fed and watered in dry weather.

 

[DirtMechanic]

It will certainly help the situation. I have sandy loam which drains very quickly and it's impossible to keep it fed and watered in dry weather.

Other side of the same coin. The buffering capacity of clay is huge and when it comes to being dry it takes an amazing amount of water to moisten it for more than a day.

 

[Mike Allen]

Soil basics. To break up dense clay. Use various aggregates. To help with sandy soils. Use vegetive composts/mulches.

 

[Mike Allen]

Sorry. Why have you used your post code. Surely Bideford would have been better.

 

[Macyard Art & Grill]

Maybe this will help.
If you have organic material that can be composted put down first (grass weeds etc) then lay on top this a couple layers of cardboard. Then top with 4 inches of top soil. Worms love cardboard and will turn it into compost. In the Macyard we have clay only 2 inches below surface/grass and the grass cant be stopped. The bonus of clay is that it retains nutrients and water well. For our vegetables we use raised beds with compost mixture and top soil but for flowers I tried mixing in some compost and made the holes bigger to allow easier root penetration but regardless everything does so well because the soil is so rich.