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Tree seeds normally have a shelf life of 1-2 years depending on species. But, it seems that the colder you keep the seeds, the longer they survive.

All the National institute of Agroforestry, will conserved seeds after doing the following process. They first clean the seeds, meaning they remove all non essential parts of the seeds. On a maple you could think of the wings as non-essential, which once clean they are called dewinged. After cleaing all the excess residue, they proceed with a three phase testing routine.

First, they will test for moisture, second they will determine the 1000 seeds unit weigth and third they will do a germination test. The moisture content test is done with an oven. Two units of tree seeds of 2 grams each are placed in aluminum containers and placed in a convection oven at 103°C for 16 hours. They determine the moisture content by taking the fresh weigth minus the dry weigth, divided by the fresh weitgh multiply by 100.The formula would be: MC % = (Fresh Weight - Dry Weight)/Fresh Weight*100. The target moisture content for most seed is between 5 and 8%. Seed that is above this range is further dried before being stored.

The second step of three is determining the 1000 seeds unit weigth. They dont usually count 1000 seeds, but they calculate the weitgh of 8 units of 100 seeds, calculate the average and multiply by 10. This calculation is helpfull for distributor but also reasearch wize, because it can give an indication of variation in seed size year over year.

The third step is to make a germination test. This will determine the seeds health and viability. First, they are place in a dish/box. The bottom of the box is covered with Kimpak, a germination paper made with regularatory requirements for industrial germination. The kimpak is moisten with water. They usually do four (4) groups of 50 seeds per dish. They then slide the tray in a rack store in a controlled temperature environnement. The temperature is 8 hours light at 30°C and 16 hours darkness at 20°C with a constant humidity of 85%.

Once these steps are done, they can now conserve the seeds. There is four levels of seed conservation. The last two ones are the one used by national institute. It seems the colder it is, the longer the seeds will remain viable.

The first level is storing the seeds at ambient temperature.

Second level is to store at fridge temperature, wich is usually 4-6 degree celscius.

Third level, is to froze at -15 degree celscius, this method will permit the seeds to remain viable for decades if the moisture level of seeds is no more then 8% but not lower then 5% at time of freezing. Normal practice is to froze seeds at -20 degree celscius.

Fourth and last is the costiest method but the most efficient. It is called cryoperservation method. Seeds are frozen at -196 degree celsicus in liquid nitrogen. This method is often used by research entities like government or national orginatisation. This method will keep seeds viable for several hundred years. For a normal person, the best way to store seeds is to keep them in a plastic/glass jar in the veggie fridge compartment.

Avid full time hobby bonsai grower. As been practicing bonsai and gardening for more then 8 years. Owner of http://www.mishobonsai.com, a website with ressource for bonsai seeds and tree seeds.