I did find one interesting article since I posted the above.

In the past, I've left conifer seed trays in my cold frame, in unknown low temps, to stratify all winter, where they stayed frozen for a good portion of that time and came through with high germination rates.

This year I'm putting some extra seed in trays in my attached garage, where it will get in the teens to twenties below zero depending on how cold the outside temperatures get this year.

With 90 to 120 days recommended stratification time for Tsuga canadensis, I already put one tray of those out in the garage. Along with a few Taxus seed.

I still have Thuja occidentalis and Picea mariana which don't need long stratification but thought about putting them out there anyways to emulate a naturally cold period they would get in the wild. Of coarse, I really don't want to kill them either, hence the question on 'how cold' can they endure.

Wondering if the ‘no freezer’ disclaimer is due to the desiccant properties that might be present in the freezer? Just a WAG.

Maybe, although in a sealed container, desiccation shouldn't occur?

I covered the Tsuga c. seed pots with plastic wrap. Moisture is condensing inside the wrap, over the cups so they shouldn't dry out, at least no very fast. Peat & perlite 40/60 medium.

I could just wait to see just how cold it gets in January. Maybe by mid/end of February, I can put the rest of the seeds out into the garage. 30 days is plenty for Thuja o. and the Picea m. is listed as not needing stratification so a month or two out there should do it.

The Tsuga is extra seed so nbd if it fails.

Google Freezing tolerance of conifer seeds and gerrminants.

Thanks Larry!

I did happen across the same article I linked to above and did glean a few things I understood but generally for me to figure out 'how cold is too cold' for certain seeds that have been soaked and ready for stratification, is a little above my pay grade. :-(

It appears to me it would have to get pretty cold before damage is done but it also appears that once seeds are soaked, they are at the most vulnerable stage of the entire cycle. And once they begin to grow, they increase in hardiness again.

Like I say, I'll just play it safe and avoid the severe cold periods with the seeds I want the most not to lose. If that makes sense? :-)

Thanks!

So once I soak the seeds for 24 hrs as recommended, I can put them out in the possibly -20f cold for stratification? I don't know if it would ever get that cold but it's possible here.

I have always stratified my seed in the refrigerator, but it would be a good experiment to see how your seeds do when exposed to possible extreme lows. I would be more concerned with higher temps later towards spring followed by more cold.

I used our limited space in the fridge last season for small containers with seeds in perlite and had good results. Too many trays for that this year.

It's good to know that severe cold isn't the determining factor between success and failure during stratification. That was my main concern.

Thanks again! :-)

Just to follow up:

The seeds put in the extreme cold in the garage did not appear to be damaged at all by the temperatures and germinated quite well.

I will most likely do this again because of the increased accessibility of the seed trays as opposed to being put in the cold frame where seed trays may be difficult to retrieve when desired. :-)