Fungal specimens are best preserved by drying.
Most people use gentle warmth which can be as simple as the top of a radiator, although purpose-built driers such as those sold for drying fruit give the best results. Large fleshy species can be placed in the air stream from a fan heater for fast, effective results even with fragile species like inkcaps.
The time taken to dry varies with the method, but can be overnight for small to medium toadstools, or longer for large toadstools or brackets. Large toadstools can become sealed by a dry layer on the outside, but leaving them at room temperature for a day allows the remaining moisture to soften this skin so drying can be resumed
Specimens are dry when they become very light weight. Then it’s best to leave them at room temperature for a day to soften up, otherwise they can be very fragile.
Spore prints should be left to dry at room temperature for 10 or 15 minutes. They can then be protected by wrapping in aluminium foil if you wish. They should be kept with the dried specimen.
A month in a domestic freezer at -18°C will kill insect pests and avoid introducing them to the herbarium.
Dried material keeps reasonably well but is attacked by a variety of pests, especially booklice and mites, and to a lesser extent museum/carpet beetles. If allowed to breed unchecked they’ll reduce Russula spp to dust and strip the hymenium off everything else including ascomycetes.
Dried material is conventionally stored in paper envelopes, but this gives no protection from insects, so the envelopes need to be stored in batches in sealable plastic bags or boxes. Avoid storing the specimens directly in individual plastic bags as static electricity from handling the bags will make extracting the dried material all but impossible.
Many people do routinely freeze their herbarium from time to time to keep it free of pests.
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BioInfo (www.bioinfo.org.uk)