I have included a few notes on the propagation of plants which, as I tend to grow hardy perennials, biennials and shrubs are not extensive. I have a cold mini poly tunnel which used to be heated during the winter to keep the frost off at which time I also raised some half-hardy plants from seed but the cost of heating and the ease with which plugs can be obtained today have proved to be too seductive a mix, particularly as I only grow a few bedding plants for containers.
Compost.I only use cheap and cheerful general purpose compost available from your local garden centre but I frequently add peat as there is no substitute for it, you would be amazed how a small amount transforms the contents of a damp bag of compost which has been at the bottom of a stack into friable material. In the case of cuttings I add a small amount of grit sand or horticultural grit to keep the drainage free.
Seeds.In general I raise most of my perennials and all my biennials from seed and I can't emphasise too much what a good method this is. Many perennial plants flower in the first year from an early sowing even though this is not always desirable when trying to encourage strong growth for a sustainable plant. The popular seed companies have started to list these separately for the more impatient among us. Most of the seed I sow is 'cold sown', fresh seed of Primulas, Meconopsis, Trilliums etc. is sown on the surface of the compost and covered with a fine layer of grit which seems to give good germination.
A rule of thumb is the bigger the seed the deeper it should be sown, where applicable I always use medium grade vermiculite or equivalent to cover seed as it helps to conserve moisture at the surface of the compost which is essential. The young plants are generally pricked out once the first true leaves emerge into single cells until the root system establishes and then into 90mm pots for growing on before planting out. Seed sown in the autumn does not generally germinate until spring, if there is germination remember the seedlings will need protection from frost. If you are in doubt seed can be stored in sealed envelopes in a cool dry place, in a sealed container with some silica gel in a refrigerator or, for the longer term, in the freezer. Dryness is the key element, seed should not be stored in such places as the greenhouse or potting shed.