A freezer is best for long-term storage of seeds although you need to make sure:
Seeds can survive temperatures that would kill the parent plant as long as they are thoroughly dried. Excess moisture in seeds that are then frozen can potentially freeze, damaging the seed.
Seeds need to be stored in a cool or cold place. Therefore, locations at floor level are preferable to those nearer the ceiling which can be significantly warmer. However, for long term storage, placing seeds in the fridge or freezer is ones best bet, as long as moisture content of the seed and storage container is low and the container is air-tight. The ideal temperature in a refrigerator is around 4 o C.
Similar to moisture and temperature, light can help stimulate and support the germination process. And, just as many foods, pharmaceuticals and chemicals rapidly deteriorate when exposed to light, so also is seed viability and vigour affected by being exposed to light during storage.
Seeds which have not been dried to the correct moisture content before being sealed in containers, can and frequently do rot. A simple test: after “drying” and placing in closed glass jars, the appearance of condensation on the inside of the jar within a few hours indicates the need for further drying. Silica gel should help with this.
Insects that may have escaped notice can wreak havoc on stored seeds. A few pinches of diatomaceous earth (DE) is a safe, inexpensive and non-toxic way of protecting seeds against insect damage. It doesn’t take much; just be sure to lightly coat all seeds before final sealing and storage. DE is available at most garden centres.
Seeds carry on life processes, at a low rate, whilst dormant. Moisture they absorb from the air combines with stored nourishment within the seed to form a soluble food, which then combines with oxygen from the air to release water and heat. Too much moisture in the air will cause the seed to burn up its stored food too quickly producing excess heat which will further lower the seeds ability to germinate. The need is to keep these exchanges to a minimum during storage to prolong life in the seed.
You must not forget that light is another of the factors that directly impact seed germination. Therefore, you must be sure that you prevent light from shining on the seeds that you will later be planting. If exposed to light, they can lose much of their germinative power. This is why at Dinafem we place our Eppendorf tubes in opaque metal boxes, which protect the seeds from light and any possible crushing or breakage during their transportation or handling.
Whether you choose to store your seeds in a refrigerator designed exclusively for their maintenance, or in a dark corner of your house, you will have to pay attention to other risks that can end up damaging them. Many experienced growers stress that seeds must be dried correctly and left under proper humidity conditions to prevent mould from appearing inside the receptacles. To keep this from occurring, in addition to drying the seeds properly, it is a good idea to always use silica gel when storing them.
Run from the light
If a container you are using is left open, and a rodent somehow gets into your house, the consequences can be dramatic, both for you and your harvest, of course, because the animal will enjoy a great feast at your expense. This is why, among other things, something as simple as placing your containers up high can be a good way to prevent such disasters.
Labelling the strains you have is even more vital if you cannot see the seeds. This can be the case if, for example, you follow the advice of some growers, who instruct more inexperienced growers to store their seeds in analogue film tubes. In cases like this you can simply stick a small label on it and jot down with a pencil the name of the strain in each tube, which should be placed, in turn, inside a piece of Tupperware to prevent its contents from deteriorating.
These are small cylindrical containers with conical bottoms, made of polypropylene, and with hermetic seals. With this method of micro conservation the containers full of seeds are protected individually, in such a way that, even if there are variations in the outside atmosphere, inside the container the humidity conditions are constant.