Guidelines for Saving Seed ...
Within the seed are all the genetic instructions for a particular plant and the reserves to get the seedling off to a good start. As they are nature’s way of preserving plants, they can last a long time. However, they do deteriorate and by storing them the best way possible you can be rewarded with greater longevity. The two factors that reduce the life of the seed are moisture and warmth.
Moisture is probably the most important factor that needs to be controlled. A dry seed will last much longer at room temperature than a moist seed in the fridge. Cool and dry are the two ideals for most of the seed we are concerned with. As a rule of thumb, the storage life of a seed is doubled for every 5°C drop in temperature and 1% drop in moisture content. There is a limit though, and freezing and ultra-drying can be harmful. The best storage conditions for home growers are 5% moisture content and the temperature of a domestic freezer or fridge.
This will depend on the crop. Details can be given for the relevant vegetable. Some are easier than others, and everyone has their favourite way to extract seed.
Water can make up between 10 and 15% of the weight of fresh seed. Drying the seed to reduce some of this moisture content (down to around 5%) prolongs the life of the seed. Heat, however, will destroy seeds and they should never be exposed to temperatures greater than 35°C (95°F). In the past silica gel has been recommended as a form of desiccant to dry seeds. The blue-indicating silica gel has now been highlighted as a carcinogen due to the addition of cobalt to show levels of moisture, and needs special conditions in handling. This does not apply to the little packets you find in various products you may buy, as that is a non-indicating silica gel and therefore contains no cobalt. There have been other indicating silica gels produced, but some concerns have also been shown on their use so we would not recommend using indicating silica gels unless new research comes to light. Dry your seeds naturally, preferably not in full sunlight and not somewhere too hot. Unless you are planning to freeze your seeds and save for many, many years then this should be sufficient for short to medium term storage.
To save seeds until the following year it is sufficient after having dried them to keep them in a cool, dry place. If you want to store them for longer periods a fridge or freezer will be fine. Use an airtight container – a kilner jar is ideal.
When you do remove your seeds from storage we recommend you do two things: Allow the jar and its contents to come to room temperature before opening. Allow the seeds to ‘rest’ for a few days at room temperature and ambient humidity before sowing. Both these factors will allow the seeds to reabsorb moisture without ‘shocking’ them, thus giving a better chance of germination.
It is impossible to determine how long a seed will last in storage. Different authorities give different lengths of time. Once the optimum storing time has elapsed germination rates reduce. However, this does not necessarily mean none will germinate. If you have old seed that you would like to grow it is still worth trying before you discard it.
Reprinted from HDRA..