Actually, in stratification, a seed needs to be kept moist AND wet for a period of time in order to germinate. I am in my final few months of horticulture technology program at college and we learned this recently.
Stratification is a combination of both moisture and cold. Chipping can destroy the embryo, scraping can intensify the stratification in artificial circumstances (ie. refrigeration vs direct sowing outdoors). Light has nothing to do with the definition of stratification.
I think some seeds need freeze/thaw cycles in order to weaken the seed coat in places, allowing water to penetrate for germination. In those cases, "stratification" can involve either periods of cold or careful chipping/scraping, but moisture is also needed at some point. So I think the only factor not involved is light... a lot of seeds need light to germinate of course, but that's a separate consideration from stratification.
Just as a note, seeds that germinate best with stratification are often great candidates for winter sowing!
I voted the period of wet because I thought there are different types of stratification and it did not say 'cold' stratification so I didn't pick the one that specifically said cold. I am pretty sure I remember some seeds need a 'warm' stratification but my memory is not always the greatest. ; )
I now realize I am thinking there are different types of stratification because some seeds need 'cold dry stratification' which still means a period of cold. So I guess I was just too busy worrying this was a trick question. I should have gone with my first instict - which was that they need a period of cold. As it seems this is most likely the official answer. : )
Strictly, none of these . . . stratification is when something (anything, it needn't be seeds) is put down into layers (Latin, stratum: layer, blanket, bed cover). A layer cake is also stratified, and so of course are rock strata and stratus clouds . . .
I was a geology/science major in college, and have only heard the term used in discussing the layers of earth. I've never heard it used in gardening before. Learn something new everyday. I can't wait to see what the right answer is.
The gardening usage derives from forestry usage, where seeds were stored outdoors over winter (to give them their winter chilling requirement) in a large container; a layer of soil, a layer of seeds, a layer of soil, a layer of seeds, a layer of soil, etc. Think in terms of a forestry nursery with 50,000 acorns needing to be stored cold and moist over the winter, before the invention of refrigeration; hence the layers. So the answer expected of us is #3.
I thought it was when a seed needs to be chipped or nicked to germinate. Interesting. Critterologist mentioned moisture, too, for this process. I'm thinking about how moon flower seeds need to be nicked and soaked in order to soften up enough to sprout.
I sure am glad you all know the terminology, and share the definitions. I can picture perfectly what you mean now.
Thanks. Thanks too, to grampapa for his contribution with scarification. I was wondering what that was called. Now I know. Critterologist is right of course that the expansion and contraction of freezing causes scarification. Just not so familiar with it where I live in So. CA.
Thanks to you all, most educational.
I got this quiz right only because I winter-sow and anyone who does so gets a short course in stratification. But I didn't really know all the details--and I loved Resin's image of all those barrels and barrels of acorns!! Thanks!
Wikipedia says that when the term is used in horticulture "stratification is the process of pretreating seeds to simulate natural conditions that a seed must endure before germination. Many seed species have what is called an embryonic dormancy and generally speaking will not sprout until this dormancy is broken."
Heh Dave usually puts the answer at the top when its a quiz. I wonder why he didn't do it this time? Maybe he's still voting in the Photo Contest (which is taking me FOREVER because they are all so beautiful sigh).
I didn't vote, but came here to see what you would all say, because during my horticulture course, stratification was used on seeds to do as MollyD suggests, which for us, involved pouring boiling water over some hard coated seeds and allowing them to soak. We also tried scarification on the same seed type to see which worked better, (by rubbing a spot on the seed with sand paper) so I though Stratification was as mollyD suggests. Thats why I didn't vote, because I didn't see the option I was looking for.
Come on Dave, put us at peace!
"Scarifying involves scratching, etching, or some sort of superficial cutting or incision. Scarification can be applied to horticulture, which involves cutting the seed coat using acid, sand paper, or a knife to encourage germination,"
This is taken from Wikipedia on Google.
Like grampapa said in post # 5775915, you have the two terms mixed up.
Stratification, taken from Wikipedia,
"In the wild, seed dormancy is usually overcome by the seed spending time in the ground through a winter period and having their hard seed coat softened up by frost and weathering action. By doing so the seed is undergoing a natural form of "cold stratification" or pretreatment. This cold moist period triggers the seed's embryo, its growth and subsequent expansion eventually break through the softened seed coat in its search for sun and nutrients."
I am with wikipedia and Molly~I think the true answer is simulating it natural weather, which, would in most cases be a cooler period more oftern as opposed to a wet one which is likely to occur at least minimally due to the weather changes in winter, even if it is only condensation. Unless you are a pine cone, then you would need fire, right? lol...
The National Tree Seed Laboratory has this pdf about seed biology with reference to different statifications: http://www.nsl.fs.fed.us/wpsm/Chapter1.pdf . Seems more to do with the mechanism to break dormancy although I thought stratification included hot/cold and other techniques like smoke treatment was a type of stratification. Resin's explanation makes sense - layered to create an environment to break dormancy. I know Davidia involucrata is double-dormant and requires several months cold, several months warm, several months cold and again warmth to break and germinate. My 2 cents.
I use cold stratification on my acorns each year to make them sprout when I start them in root pruning trays about the 1st of the year. It usually takes about 90 days for them in the bottom of the fridge. I usually rinse them off in some warm water first so I guess they have enough moisture in them to do the job. They always start sprouting within a week or two.
I have heard of scarification when starting hard seeds such as persimmon and hickory nuts, but have never had the opportunity to try them.
LOL.. here, I don't start winter sowing until February. We often get some "unseasonably" warm weather in January, followed by very low temps... seeds sown now would probably sprout and perish! (but I understand your impatience)
I have always called the process that I do with Blue Bonnet seeds, 'torturing them' that is when they are put into water, and frozen, then thawed and re-frozen and then planted...it seems to work with Blue Bonnet seeds they have a very hard seed coat...there was a man, some years ago...who would put seeds for the Blue Bonnets in a cement mixer...I guess that would be scarification...that seems to work too.