Posted: 15/02/2014 at 18:01
For the lawn area, if you can rotovate or fork in about 3 inch of compost, or well rotted FYM into the top 6 inches of clay, that will do. My brother bought a house with a lawn of turf laid over clay. The turves curled up like old sandwiches. He stripped the lot, pinched the entire contents of my mums compost heap, all the used tomato compost etc, and rotovated it in. He then seeded it, and now has a nice lawn.
To plant shrubs, mix organic stuff as above with the clay in a 50 /50 mix, and make the hole for the root ball at least twice as big as the plant root ball. Otherwise you will plant into a sump and it may rot in wet weather.
Clay can be very productive if you can get enough organic matter into it.