>> Emerging science suggests that long term storage of seeds in plastic containers can reduce the shelf life of seeds.
I would love to find out more about why plastic would affect seed viability after long-term storage. I'd appreciate anything you recall about the sources or their reasons, so I can follow up. Volatile plasticizers?
Right now I store seed in 2x3 Ziplocs bundled inside other Ziplocs and glassine envelopes, inside plastic tubs (usually with some desiccant). I open the tubs very often.
The only downside of plastic storage that I know about is that plastic can trap humidity inside, if the seeds were not dry enough to start with. And even dormant seeds metabolize slowly, so they produce tiny amounts of humidity over several years.
Or, even dormant seeds use a tiny amount of oxygen. Perhaps any
very tightly sealed container that has
very little air trapped inside might run out of oxygen over many years, and then the seeds would suffocate and die. But that seems unlikely in most situations since seed banks seal seeds totally hermetically in Mylar pouches or glass vials.
One thing about Ziplocs as opposed to freezer-bags or Seal-A-Meal bags that are melted shut, is that Ziplocs are pretty leaky. The "zipper" is pretty loose, and both humidity and oxygen can diffuse slowly right THROUGH most kinds of thin plastic.
(* Footnote 1)
You can prove to your self how leaky Ziploc zippers are. Seal 3-4 small Ziplocs, trapping some air inside each one. Stack them up on a desk or table and press your palm against the stack of "bubbles". A little firm pressure will squeeze air out right through the closed zippers. That means there are gaps that gasses can diffuse through.
The main factors that I know of for keeping seeds viable for more years than usual are:
- dry humidity (prefer 15-30% RH)
- cool temperature (4 degrees C = 40 F) (or a cryogenic freezer)
- dark (this is a lesser factor)
(Also, they seem to prefer unvarying conditions over swings of temperature and humidity.) (* Footnote 2)
======================
(* Footnote 1)
https://secure.drierite.com/ca...
"While the plastic film will hold liquid water, water vapor may pass through it. For instance, 1-mil polyethylene will pass water vapor at the rate of 1.5 grams/sq. ft./ 24 hrs, while 4-mil polyethylene will only pass about 0.05 grams/sq. ft./24 hrs at 75° F and 100% RH. "
(* Footnote 2)
Post-harvest handling of seed collections
http://www.kew.org/sites/defau...
Some more links:
Kew Millennium Seed Bank Project, long-term seed storage containers:
http://www.kew.org/ucm/groups/...
Kew: theory of desiccants and RH
http://www.kew.org/ucm/groups/...
Many Kew Royal Botanic Gardens Technical Information Sheets about collecting and storing seeds, written by Millennium Seed Bank staff.
http://www.kew.org/science-res...
"Giving Seeds What They Need In Storage":
http://www.hillgardens.com/sto...
http://permaculture.org.au/201...
http://www.cog.ca/documents/Se...
http://www.seedsave.org/issi/9...
