Storing Seed for Best Shelf Life

I'm such a dunce sometimes! For many years I have bought OP (open pollinated) and/or Heirloom seed, both for the interesting varieties, and so I could save seed for the next year. It never occurred to me to look into how to store them in the best possible way, simply because I never looked beyond next year's garden... and my seeds were "mostly" viable for the next year.

Since I had not planned much of a garden this year (until recently) I only had a stash of old seeds pre-2010, and no new seeds on order. Now that I have researched the longevity of some seed varieties with optimum storage, I'm pretty sure a lot of the old seeds I have are now duds. I always save tomato seeds but the last 2 summers have seen all my tomatoes fail with NO seeds to save, so any tomato seeds in my stash are at least 3 years old.

As it turns out, tomato seeds are among the longest lasting when stored properly, so I still have a tiny chance of some germination. All my seeds have been stored dry (necessary to extended life), but not stored cool (also necessary). That will change this year as I am now determined to store all my seeds properly.

I did order seeds last week. However, most seed packets come with many more seeds than I need to plant, so this year I will properly store unused seeds instead of just taping the packet shut and dropping the packet in my seed shoebox!

Two main things affect the storage life of seeds. One is their natural longevity, and the other is storage conditions, which include temperature, humidity and light. Remember, seeds are alive!  What you want to do is store them in the opposite conditions that are suitable for growth... seeds germinate with warmth, moisture and light so you want to keep them cool, dry and dark.

Some seeds simply do not store well even in the best of conditions. Those primarily include onions and peas, but also corn, grains and beans. 

Seeds that store the longest:

Crucifers: broccoli, cabbage, radish
Nightshades: tomatoes, peppers, eggplant
Melon family: zucchini, watermelon, pumpkins

Best Seed Storage

First, seeds need to be dry initially, and then kept dry and in the dark. Storage conditions of less than 50% RH (relative humidity) are best, but not too low or the seeds will dry so much they are virtually dead. You can achieve low humidity with seeds in jars by adding some packages of a desiccant like silica-gel (those little packets that sometimes come in potato chips, or leather goods). Silica gel crystals are usually blue, and they turn to pink when they have absorbed moisture. You can put them in the oven to drive off the moisture; they will turn blue again and can be re-used. Survival foods sites sell them.

Secondly, seeds need to be kept cool, under 50ºF. You can store seeds in the refrigerator, the freezer, under the house in a crawl space, or in a root cellar, any of which greatly extend shelf life. I will store mine in the freezer until cool fall weather arrives, then they will go in the root cellar to free up freezer space for fall butchered meats.

I plan to vacuum-pack all my unused seeds in their packets. That way I can toss them in the fridge or freezer and not worry about any absorption from anything else. Seeds I will save from this year's crops I may put in canning jars with some silica-gel packets until I'm sure they are fully dry. Then they can go in the root cellar.

Here are some helpful links:
Giving Seeds What They Need In Storage - good, commonsense information for the home gardener 
Seed Storage Tips - the basics for home gardeners
Seed-Storage Times and Viability

Interesting tidbit: 
Out of about 10,000 edible plants, only 120 (about 1%) provide 90% of the food worldwide!