Timing
The optimum time to collect seed from most subjects is when the seed capsule becomes ripe and turns brown. In most cases this will involve nothing more complicated than picking the capsules from the specimen and placing them in paper bags or lined seed trays. However, with a few species such as geranium and vetches, which flick out their seed as soon as it becomes ripe, you may have to tie a paper bag round the stems in order to catch it.
Cleaning seed is often a straightforward process, for example foxglove, verbascum and aquilegia seeds literally pour from their capsules. Others however, such as honesty, aster and dianthus may need to be broken up before the seed can be picked out. Blowing on the seed to separate it from the chaff, a process known as winnowing, is often the best method, but you can also use a series of sieves, each with varying grades of mesh, to make this process slightly easier.
Cleaning
The seed of many trees and shrubs is often encapsulated by a succulent berry or fruit. Where this is the case, for example with crab apples and medlars, pare away the hard flesh before extracting the seed, or squash the soft berries, in the case of berberis and cotoneaster, before swirling the whole lot around in a jar or bucket of warm water, decanting off the pulp and adding fresh water as necessary. Most of the flesh should come away from the seed, but you can pick off any remaining when it is dry. Once cleaned, all seed should be clearly labelled with its name and date of harvesting.
Green Seed
Most seed is collected when brown and ripe, however some such as Daphne mezereum, primroses, snowdrops and anemones, are best gathered and sown when they are still green. At this stage the seed will be anatomically complete but long-term dormancy will not have become built-in and so germination will take place far more readily.
When to harvest seed from the wild:
If the seeds are contained in capsules, like poppies and corncockles, you can take one off the plant and tip it up: if ripe, the seed will fall out cleanly into a container. Some capsules won't empty by tipping and they may need crushing to release their dark, ripe seed inside. (If you are collecting harebell, take your glasses because the seed is like dust) If the seed is still green or moist, leave it for another week or so. Primrose is trickier as the seed-head is on a long stalk which bends over on to the soil and you have to look carefully to see which heads have turned brown. Collect these seed-heads just before they open - otherwise the seed will just fall to the ground.
Seed storage depends largely on how a particular type of seed stores its own reserves of food. The majority are dry seeds which store their food as carbohydrates and, under ideal conditions, will remain viable for two or three years. Fleshy seeds such as horse chestnut, lilies and peonies, which store their food supply as fats or oils, will, at best, survive a year. To avoid problems, it is best to collect these latter types just before they are dispersed and sow them in a polythene container to retain moisture and place them in a fridge to slow their natural metabolic processes right down.
Dry seed does present fewer storage problems and can be placed in paper bags or envelopes in a cool spot such as a cellar, attic or garage. For protection from damage caused by vermin or moist atmosphere, place the individual packets in an airtight container with silica granules added to remove the excess moisture. Avoid storing in polythene bags as they tend to seal in moisture which could result in rotting.
Gourds can certainly make attractive and interesting decorations. Try to protect them against early frosts as the fruits start to reach maturity by covering them with horticultural fleece or even old net curtains or newspaper. Using a cloche is even better as this will also help to speed up the ripening of the fruits. Use a sharp knife to cut the gourds from the plant - it is important to do this rather than just twisting or pulling them off as any damage to the stalk will reduce their keeping quality. Put the gourds in a warm, dry spot such as a spare shelf in the airing cupboard or in the greenhouse. After about three weeks, remove the gourds and wipe their skins gently but firmly with a non-bleaching disinfectant solution. Then leave them to dry off over a period of a few hours. When it comes to polishing them, any good quality wax will do but it seems that car wax produces a better finish than a floor polish. Alternatively, you can varnish the fruits, but waxing provides a more 'natural' effect. You should find that your gourds will last for several years with only a very slight loss of colour.
