How to store seeds properly and work out if old packets are still usable

Seed catalogues are starting to land on our doormats now – often while gardeners are still sorting out and storing or discarding seed packets left over from this year. Seeds mostly last for several years if they are kept cold and dry. Dry, unheated rooms indoors are satisfactory, but dank sheds can quickly kill them. Ideally store seeds in sealed jars or boxes with some drying agent. Silica gel is best and widely sold online. However, rice, which is often recommended, is ineffective. Space-permitting, a fridge or freezer is ideal – seeds can last for decades in the latter. This is true even of dry seeds of tender plants that are usually killed by frosts, such as tomatoes. Store in plastic bags or boxes and, when ready to be used, allow the seed packets to reach room temperature in a sealed bag to avoid condensation. Shorts Some gardeners sow what they need and discard the surplus seeds that remain in the packet. To them, new seed seems inexpensive compared to the work and expense of raising plants and the disappointment of failures. However, good seed is expensive and to other gardeners the risk of failure when storing opened packets is acceptable. In these cases, storing seed away immediately after use and not leaving it in sheds or, worse, greenhouses, helps to keep the seeds viable. Unopened packets, especially if the seeds are in sealed foil, last longer. Being optimists, gardeners tend to over-buy, leaving some unopened packets bought with high hopes, but which they never got around to sowing. There is always next year. Smaller seeds are shorter-lived than larger ones, but there are exceptions – dust-like nicotiana and begonia seeds can last several years. Acorns, chestnuts and beech mast lose viability if stored dry, and must be sown in the autumn while fresh. Freezing them is also ineffective, unless in liquid nitrogen. For vegetables, cabbage family seeds last at least five years in unsealed containers in a normal room. Leek, lettuce, onion, parsnip and sweetcorn seeds are short-lived. Reliable information on how long flower seeds remain viable is harder to come by, but most will last three years. Seed suppliers may not themselves buy fresh seed each year, but keep a batch for a few years, hopefully stored in good conditions, taking some out each year. Eventually it no longer passes their germination test and they have to buy fresh supplies. Therefore, buying new seeds of short-lived species each year is wise. Home-saved seeds are often much more vigorous and long-lasting than bought seed, as packet seeds necessarily take some time to reach retail outlets. These seeds are mostly grown abroad and must travel along often lengthy distribution networks and supplier warehouses and testing facilities. However, there are practical limits to how many home-saved seeds gardeners can produce, and hybrids are impossible to home-save. Begonia seeds can last for years (Photo: Mandy Ellison-Tout) Seed legislation gives gardeners some protection. To be legally sold, vegetable seeds must meet certain standards including minimum percentage germination, such as 65 per cent for carrots and up to 80 per cent for turnips. Flower and other ornamental seeds are covered only by consumer law. Having said this, most suppliers will replace failed new packets free of charge. Once you know how many old seeds you can use next year, it is time to consider new ones. Look out for the RHS Recommends Award of Garden Merit logo, which indicates plants that have excelled in evaluations of how well plants perform under garden conditions. Also be ready to take advantage of clearance sales. The seed might be intended for this year but, properly stored, it should grow well in 2027. Guy Barter is the Royal Horticultural Society’s chief horticulturist. @GuyBarter The RHS is a charity inspiring everyone to grow via its research, advisory, outreach, shows and gardens. For more information, visit: rhs.org.uk