Well rotted manure helps break up clay soil, but should be added in autumn for best results. Could you leave the really claggy bit for this summer and work on it in the autumn/winter ready for 2009? I have also added sharp sand but have been told that this is not as effective long term as the particles sink into the clay without breaking it up.

I have built (along with most others on the allotment site) a number of raised beds filled with imported soil/compost as the soil is very heavy clay.

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Julie