>> Seems to me the desiccant would draw any moisture from the air TO THE SEEDS. :-)
That's not my understanding of silica gel, although paper and cardboard MIGHT work that way. (Trap condensation or humidity when the air is very damp, then release it near the seeds.)
Silica gel just absorbs humidity and won't release it again until you heat it up to 250F or so. Maybe some other desiccants are more like cardboard than silica gel: humidity BUFFERS rather than humidity TRAPS.
But I seal the desiccant in with the seeds, and
seal air out (that's why I mentioned that I would use double-bagging). If you don't seal air away from the desiccant, it just absorbs as much water as it can hold and then sits there, inert.
I think that very few gardeners bother with desiccants. Many of them still save vegetable seeds for a year or two or more. Some big seeds can be saved for five or more years in fairly dry climates.
I go by what some pamphlets from Kew Royal Botanical Gardens said: that viable seed life may double for every 10% decrease in relative humidity that is maintained steadily.
However, I'm not consistent about keeping the desiccant fresh, so I'm probably not getting the full benefit anyway.
post-harvest handling for seed collection:
http://www.kew.org/sites/defau...
"Seed life span approximately doubles for every 10% reduction in seed eRH."
("eRH" is equilibrium Relative Humidity.)
(Middle column, near the bottom of the first screenfull on my browser.)
" Once transferred to the seed bank, collections can then be dried to around 15% eRH (4-7% mc depending on seed oil content), the recommended moisture level for long-term conservation of orthodox seeds.
("mc" is moisture content , % water by weight.)
