Seed can be expensive and saving your own takes time, so it’s worth putting some effort into storing your seed well, to keep it as fresh as possible until sowing time.
For the seed bank at the Botanic Garden, we collect, dry, clean and store seeds of wild Welsh plants for future conservation and restoration uses.
Some of the techniques we use in the seed bank can be applied to storing seed in the home – here are some tips.
The two key conditions for seed storage are dry and cool. Excess moisture and warmth causes seeds to lose viability and encourages fungal outbreaks or rotting.
It may come as a surprise that seeds are porous, equilibrating with the moisture content of the air surrounding them. On a cool wet day when the air is humid, seeds will take on moisture, and on a warm dry day, they will give moisture out.
Keeping seeds dry
The trick is to make sure your seed is fully dry and then keep it dry, by storing it inside an airtight container.
Numerous paper seed packets can be placed together in a large container. A glass kilner-style jar is ideal – having a lid with a rubber seal and clamp, they seal very well and are even used in many professional seed banks.
Plastic storage containers with seals are also suitable, although they do let some air (along with moisture) in over time. For short-term storage, ziplock bags are also possible, but I’d recommend using two zip lock bags in case of any air leaks.
To absorb excess moisture, add some desiccant (drying agent) to the bottom of your storage container.
Silica gel is excellent for this and can be bought online. We recommend orange colour-changing silica gel, which turns green when it absorbs moisture, giving an indication of when moisture has entered a storage container. The silica gel packets found in new product packaging, usually thrown away, can also be used.
Calcium chloride, used in dehumidifiers, is another suitable desiccant that can be easily bought. Oven-dried rice is a low tech alternative.
Replace or dry the desiccant periodically when it gets moist. Remember that each time the container is opened, humid air may enter. Storing breathable packets inside the sealed container means the desiccant can absorb the excess moisture from the seeds.
Keeping seeds cool
A fridge is an ideal place to store your sealed container – a cool temperature of around 5°C will slow the ageing process in seed, maintaining viability for longer.
Although fridges are very humid (think of the condensation that often forms inside them), the airtight containers will keep the seeds dry. If you’re unable to store in a fridge, find somewhere dark and cool.
How long will seeds last?
Storing seed in this way will keep most seeds viable for a few years, although it is always advisable to use seed as soon as possible after harvesting, as a decline in seed viability is inevitable over time.
Plants vary in how long their seeds stay alive – parsnip and sweetcorn, for example, are best sown within a year of harvesting, whereas runner beans and lettuce can last many years if stored well. Garden Organic has some really good guidelines on saving seed from vegetables.
This blog was written by Dr Kevin McGinn, Science Officer for the Growing the Future project.
This project has received funding through the Welsh Government Rural Communities – Rural Development Programme 2014-2020, which is funded by the European Agricultural Fund for Rural Development and the Welsh Government.