https://www.gardeners.com/how-to/grow-sweet-pea-flowers/7263.html

i did not have time to study this.. nor watch the vid.. hope it helps

ken

The plant can tolerate 25 degrees. The seed can tolerate much colder (but the 9 would be a problem in a flat and I probably wouldn't risk the 20s when they've been seeded for a bit). I'd definitely protect them from deep freezing at this point, but you don't have to be so gentle with them later. Even the seedlings are tolerant of a light frost.

However, just to be safe, and since everything is in a flat (where temperature moderation isn't what it would be in the ground), I'd put the absolute bottom temperature at 35 degrees. That gives you some room for "whoops, the weatherperson was wrong" but definitely wouldn't allow for root freeze no matter what happened.

Thanks! They will go in the greenhouse. How I wish for once the weatherman would be wrong but doubt that will happen. Polar vortex is to hit us at 3pm tomorrow - so I will bring them in and protect them. The ones I planted in the ground may not fare so well, but at least I can save these!

The ground ones should be fine! If you could put a layer of mulch over them to protect them from the single night of nine degrees, that would help. Even dropping old newspaper over the top would be a significant help. Pin several layers down with rocks. And if you have a few inches of snow cover, even better. Soil temperatures probably won't significantly go under 32, and the seeds won't care.

But the twenties aren't going to bother sweet pea seeds any in the soil as long as they've not sprouted significantly (and they probably haven't).

I gave you "overkill" instructions on the flats just to assure that the ground in there doesn't freeze and then go even colder. At 9, it probably would. In the twenties...well, maybe, maybe not, but there's no reason to take chances.

(Right now, current air temperature is 19. We have a foot of snow cover, my exterior sensor is buried, and the temperature 3" off the ground under 9" of snow or so is 31-32 degrees and it hasn't moved in days. Snow is an excellent insulator).