This question was prompted after watching MIgardener trying to germinate 87 year old seeds. Hopefully they germinate and thrive!
Now I’m no master gardener but I’ve read a few studies that suggest it’s actually injurious for dry and low moisture content seeds to soak them, especially if cold or hot and anaerobically soaked. These seeds may germinate well but the plants don’t thrive as well as they could with damage to parts of the plant like the cotyledons (first leaves).
So it’s probably best to keep your seeds in their Goldilocks zone by getting the temperature and moisture just right. If you’ve ever dropped ice in a warm glass of your favourite drink and listened to it creak and crackle and crack as the ice thaws quickly, this is what you’re effectively doing with seed soaking at the wrong temperature or moisture levels.
Ideally a warm humid environment where the seeds and water can come up to the same temperature and moisture content at the same time, is ideal to start the process. Placing both in a container somewhere that meets the temperature requirement for those seeds to germinate is ideal. Seeds germinate best in 100% humidity and some like it hot, and some sweat when the heat is on. Find that Goldilocks zone. Once their in that zone you can wash them or briefly soak them and inoculate them if you like.
Soaking also leaches sugars and other compounds that seeds would otherwise use to create a fertile environment around themselves in soils. Some practices that remove the seed coat also injure the seeds, but remember all seeds are different and a germinated plant is better than no plant. There are no hard and fast rules. Find what works.
I’ll leave you with the following quote from a 1919 Dwarf Red Bean study by Franklin Kidd and Cyril West:
“Soaking these seeds for periods up to 24-48 hours at ordinary room temperatures increased the rate and vigour of germination; but the effect under the conditions of the experiment upon the subsequent development of the plants produced was injurious, even in the case of short periods of soaking”
They knew this in 1919 and yet it’s still common practice to soak seeds.
So please, don’t leave your seeds cold and wet outside, or inside, that’s no kind of atmosphere for them.
And here’s to having fun, fun, fun in the sun, sun, sun!