Re: Do I have to buy new garden seeds every year? Seed viability?

You ask a lot of interesting questions. For all of your questions, it will 
often depend on the species and the storage conditions. Most flower and 
vegetable seeds will remain viable for more than one year so leftover seeds can 
usually be used the next season. However, seed germination percentage will 
decrease with age. 

For long term storage, most flower and vegetable seeds store best in a freezer 
in a sealed plastic container containing a dessicant, such as silica gel. For 
desiccation-tolerant seeds, a seed moisture content of 5 to 7% by weight is 
considered ideal for long term storage. Some seeds are dessication-intolerant 
and cannot be dried that much.

Seed producers do not say a lot about seed longevity because they would prefer 
you buy new seed packets every year. Generally, you expect seed packets to 
contain seeds that were just harvested after the last growing season. You might 
want to contact some seed companies and ask them what their practices are. Seed 
packets usually are dated with the year they were packed for and have a 
germination percentage.

Check the "Guinness Book of World Records" to find the record for seed 
longevity. Some buried lotus seeds were found to be over 1,000 years old and 
still germinated. However, some people have questioned if the seeds were truly 
over 1,000 years old. In 1879, Professor Beal of Michigan State buried jars of 
20 species of weed seeds and 100 years later three species still germinated. In 
1947, Fritz Went started a 360 year study of California plant seed longevity by 
vacuum-sealing 91 species in glass tubes and storing them at 20-25 C. After 50 
years, most species still germinated. 

Vegetable seed longevity varies depending on the website, presumably because of 
either the storage conditions or the minimum germination percentage accepted. 
One site says longevity varies from 3 years (lettuce) to 7 years (snap bean) to 
14 years (parsnip). Another website says parsnip and lettuce last 1 year, with 
a maximum of 5 years for cucumber (see reference websites).

Most states have state seed testing laboratories. You might want to contact the 
one in your state.


References



Storing Vegetable and Flower Seeds




Storing Seeds for Longevity



Fritz Went's Seed Longevity Study


Vegetable Seed Longevity