Clay is a fertile soil but it can become water-clogged. Check the drainage by digging a deep hole or two, and seeing how quickly they empty of water, after rain.
Sand or gravel, compost too, added to clay will improve its drainage.
If the soil tends to get very waterlogged you may need to run earthenware land drains to carry surplus water away. They need to be put in a foot down and should slope to a soakaway.
Dig clay soil over roughly at the beginning of the winter. The frost will then do the work for you, by breaking up the heavy clods into a finer tilth.
Light sandy soils drain too easily- the rain washes nutrients out of them. Help stop this happening and improve the state of the soil at the same time by adding compost, peat or farm manure.
Do not dig sandy soil in the autumn- winter rains will leach all the goodness out. Never dig it deeply either. Just fork it over in the spring, adding compost or manure.
Free compost is easily made from waste garden and kitchen scraps. Build up a heap, spread lime over it every few inches or so. Cover with plastic sheeting or sacks and leave for 2 or 3 months to rot down.
Grass clipping put on a compost heap heat up very quickly and accelerate the decomposition time. Commercial activators help speed up compost making. But just a thin layer of stable or farmyard manure will do the same job.
One large compost heap is better than two small ones- it heaps up faster.
Your compost not rotting down properly? It’s probably too much or too little water and not enough air. Turn it over with a fork.
Mulching- scattering vegetable material like straw, peat or grass clippings over the surface of flower or vegetable beds is a great free benefit. It holds moisture in in summer, discourages weeds by smothering them as they come up, and rots down eventually to add nutrients to the soil.
Some plants-notably rhododendrons- hate an alkaline soil, so check yours with a soil testing kit to find out its pH. The best all round figure is 6.5, lower figures mean the soil is acid, high figures, alkaline.
Alternatively, the cheapest way to check on your soil is with litmus paper from the chemist. Make up a thick solution of soil and rain water and dip the paper in it. If it turns red the soil is very acid(below pH5), yellow, medium acid. Yellowy-green is a good average soil and blue strongly alkaline.
Over-acid soil can be corrected to some extent if you add lime to it in the autumn. A soil testing kit will tell you the correct amount for your ph.
An alkaline soil is more difficult to correct: use acid-producing fertilizers such as sulphate of ammonia on it, add peat and powdered sulphur too.