Thread: Hard Clay Soil Under Lawn...what to do?

I had my house built 2 years ago on a 940 sq/m block. All of the land is grass that was left to grow through the soil after the building work.

The problem I have is that the soil is rock solid..the area is known for having high clay content.

Now when I say hard, I mean HARD. In the patches where grass is bare, I attempted to use a garden fork to put aerate the soil/lawn. I couldn't even get the fork into the ground, not even one inch in, with all my weight on it, even soaked soil is impossible to penetrate.

This is obviously why the grass is very patchy in areas.

Drainage is also terrible..water does NOT soak into the ground at all...I've laid some trenches with gravel, leading into the water tank overflow pipe that leads out onto the road kerb...this has helped a little.

When the soil is dug up (after a lot of back breaking work)...the soil is almost pure clay...even if its soaked and dug up, it's like really thick modelling clay..not at all like soil.

Now my question is, is there anything I can do to the soil to help break is down somewhat, to help the lawn grow easier?

Gypsum keeps popping up in my searches, but can this be spread over a lawn, and will it do anything if it cant be dug in?

Any help would be very much appreciated, as I have no idea what else I can do...

Gypsum would be the answer, but it needs to be dug in, and will take time. If you can add compost etc would be good.
Other option is to buy soil from your local supplier. (or a bit of both to speed it up)
The way it works is this. The developers strip all the topsoil from the new estates and sell it to the landscape suppliers. The new owners (after the estate is sold off) want gardens so they go to the suppliers and buy the soil back...almost everyone's happy.
TM

I had the same problem exactly. I actually left it for 2 years and not 1 weed grew in it, it was that hard and dry.
Here is what you need to do.

Firstly, go and hire a rotary Hoe. not a small crappy one, get the big diesel powered one.
Go and buy a few bags of mushroom compost (the more the merrier). Some aged chicken manure (maybe 1 bag) some blood and bone a few bags of gypsum and a few bags of sand.

Spread the lot out over the area of your dry clay. doesnt have to be neat.
Get the rotary hoe, fire it up and start walking up and down and around the area until its all chopped up and got some air in it.
Dont be afraid to put all ur body weight on the rotary hoe and really get it burried to loosen everything up.
the hoe will mix all the stuff you threw down, and what you've done is the following.

1. Mushroom compost - add organic matter to the clay soil to feed it nutrients and allow it to decompose and improve your soil
2. Gypsum (takes ages to work ) break up the clay
3. Sand to lighten the clay up and allow better drainiage between particles
4. Blood and bone - some food
5. Chicken manure (dont put too much just sprinke some around) will give it some food

Finally, get some seeds, go absolutley nuts with the grass seeds, and lightly rake it all nice and flat. Dont worry bout compacting it all down, let the rain do that for you but the raking will get the seeds belwo the ground slightly to germinate and grow well.
I did this in my front and back yards and the results are amazing, i have green lucious grass and the clay soil is now going a nice black and worms are imroving there. once u get worms in, they will do the work for you.

Cheers

I would second adding vast quantities of organic material - several times. If you want something in addition to lawn (like a garden) then you can try no-dig gardening - layers of wet paper or cardboard, layers of manure, layers of straw or cane mulch, then pockets of potting soil to poke the seedlings into to start them growing. Spuds are a great crop to get the ground broken up a bit too.

Thanks for the replies guys...

I should add (I thought I had) that I do have a full lawn of grass (but is thin/bare in places because of the rock solid clay soil).

It would be a shame to have to churn all that back up...but it seems like this is the only real solution...?

Also, the size of area I would need to do this too is rather massive and would take a LOT of work...might be worth trying one area and see how that turns out I guess...

Do one area at a time then, I will re-iterate the previous advice.
Organic matter in multiple cubic meters, old newspapers etc:

Gypsum, lime, the product sold at Bunnings ( Clay breaker a smelly black liquid ) all the compost you can scrounge or buy, dig pits and fill with all of the above.
If you need to; find a powder monkey and use explosive to dig the holes and NO I am not joking; it works very well.

Clay holds great quantities of water and nutrients so you are lucky in that respect, soil needs lots of organic matter so sheet mulching and raised garden beds for vegies

Hey all,

Dont want to Hijack, but I am in a similiar situation where I have an established lawn but a really bad clay soil, throughout winter it became extremely squishy under foot and has finally started to dry out.

I was thinking of coring it and then filling with gypsum and top dressing it with this at the same time. What else should I mix in with the Gypsum to do this? and is it the right time of year to do it?

Cheers

Robbo

Don't bother coring, it works but only in the cored bit, rotary hoe or dig it by hand NOW, before it sets rock hard, a little dolomite helps as does any sort of organic matter, sawdust, shavings, shredded newspaper all dug in with the rotary hoe.
Then sheet mulch or plant a green manure crop, go to the supermarket and buy a few big bags of green lentils, Borloti beans, chickpeas red kidney beans soak them overnite in lime water and plant them in the freshly turned soil, cover with a thin layer of earth and keep the pigeons off until they sprout.

In 5 or 6 weeks dig them over again and add blood and bone, a little more dolomite and a little more gypsum.
I don't have a lawn, just grass in odd patches I am gradually putting in either productive raised vegetable beds or deep mulched no dig native gardens.
Takes about 3 or 4 years to get the soil fixed by this method but it lasts for 50 years, just a little fertilizer and trace elements needed each growing season

Using Gypsum really isn't the best option in many soils and I often say for folks not to bother.
I think you'll find that Dolomite of Lime will be more effective but only with the addition of certified organic composts. Using chook poo means what ever you plant will bolt and produce loads of leaf with little root structure to back it up. That is going to wipe the smile from ya dial when things start getting fungal disease or just get hard to get right.
Nutrient leaching can also be quite significant from it and that can harm waterways where those nutrients will eventually find them selves.

It is ultimately fulvic, humiic and amino acids that will get that clay broken up. These are found in powerfeed and for this reason it is said that 10ltrs of Powerfeed will do now what 1 tonne of Gypsum will do in 3 years time.

Certified composts generally don't smell and have a much higher quality than what most people encounter down their local landscape yard