[boldondig]

I know it has been said before but I had a similar issue and looking back the best two things I did were ;-
 1. Buy a mattock - got mine with a yellow plastic handle - cost me £20 - but it is the only thing to break up at the clay, hand a lot of use and still going strong.
 2. Got to know local horse owner and got barrow loads of manure to dig in every autumn.
The only other thing you need is patience....will take a few years to get the soil in good shape - but it is worth it - I get great veg now.

[BigPaddy]

The product Dumpling was trying to remember is called Gypsum. There is a commercial one called Clay Breaker but I suspect it is the same thing but more expensive. Liming will help but, as mushroom compost usually contains lime as well as manure/straw, try and get some of this - two for the price of one! 

Good point.

[JayG]

Gypsum is about the best flocculator of clay there is, mainly because it's more soluble than many other common calcium salts, and has the added benefit of not altering the pH of the soil one way or the other.

[Headgardener22]

Liming will help but, as mushroom compost usually contains lime as well as manure/straw, try and get some of this - two for the price of one! 

I used mushroom compost for a couple of years and it did make a difference. Can't get it any more as the company I used to buy it from went out of business - beaten by Polish and Irish mushroom growers.

[jaydig]

I had my plot six years ago, and found out that the topsoil had all been removed a few years before that by the local council, leaving heavy, clay subsoil, with no life in it, and no worms to speak of. The few worms I did find were 'grey' looking and very sluggish. Six years, tons and tons of manure, hours of back breaking work smashing away at it with a fork, and removing stones, brick ends, etc., the soil is now a lot better. Its fertile, and  there are loads of very active worms, although if it gets too wet or too dry its a problem to dig. I made three compost bays and compost absolutely everything except the really nasty perennial weeds, which I burn and then add the ash to the compost bays. Keep chipping away at it and it will gradually get better.

[Middlesexbloke]

Some great posts here, has helped my understanding as I too have lovely London clay soil plus lots of gravelly stones lol. Very fertile though! I dig in lots of compost and manure but when planting seeds directly I still need to make drills/holes and plant into compost. Guess it takes years to get a nice friable soil lol...

Just back from the plot and was chatting to a neighbour about the clay soil. He said the thing that worked the best by far was digging in loads of mushroom compost. Will be on the lookout this Autumn

[Headgardener22]

I found you had to dig in mushroom compost every year. If you miss, the soil reverts to type.

[Middlesexbloke]

I found you had to dig in mushroom compost every year. If you miss, the soil reverts to type.

Interesting, thank you for that. Was hoping the mushroom compost would alter the structure for at least a couple of years!

[compostqueen]

You need to make lots of homemade compost and get a leaf mould bin started. Also if and when you have an allotment bonfire, save the ashes as these help with the job of lightening soil structure.  I have a Chillington hoe which I find very good for knocking big lumps of soil on the head

Good luck with it 

[Anton]

Yes, the idea is to incorporate as much organic matter every year. One thing I did, maybe a bit excentric, was just to turn the patch I required just before planting and sewing and then placing the weeds from that part on the patch behind me to keep the soil underneath moist until I was ready to use that patch and so on.

Anton

[NewSteve]

Top marks to the council who took the topsoil off the allotments 

If there are parts of the plot you don't need to use this year, you could try sowing a green manure. There are some that have deep roots and will help to break up the soil for you. This looks like a good reference:

http://www.greenmanure.co.uk/advice/choosing-the-right-green-manure/

[Headgardener22]

I found you had to dig in mushroom compost every year. If you miss, the soil reverts to type.

Interesting, thank you for that. Was hoping the mushroom compost would alter the structure for at least a couple of years!

It depends how much you put on. What I said was a bit black and white. When I put 9 inches of mushroom compost on one small area, it lasted two years but anything less than that didn't work.

Garden compost & leafmold however, seems to work a bit better, it doesn't seem to breakdown quite as quickly.

[Goosegirl]

I echo HG22 regarding how quickly mushroom compost breaks down, but it is good stuff, smells lovely, and you get a free crop of mushrooms as well!