Resistance of germinating seeds to mild frost temperatures

I’m sowing my seeds. Fresh out of the fridge. Some floribunda crossings started to germinate. Not much, just the root sticking out. I’ve put these into small pots (3.5" diameter). Covered with half an inch of soil and some white sand.

These pots with germinating seeds I’ve put in my (cold) greenhouse and we’ve got some frost at night. My greenhouse lost 2 windows due to a storm and so it gets as cold as outside at night, but the containers are out of wind and rain and such. Temperatures at night are 29°F (-2°C).

I think those germinating seeds should have some built-in protection against mild frost. They’re still covered with soil. Am I doing good or should I take them inside. I could use some confirmation.

1 Like

Everything I’ve ever read about rose seedlings has stated they are highly frost resistant at least until they develop their first true “rose leaves”. Most roses, with the exception of really tender types, are easily hardy to 29F. You usually don’t have issues until you reach significantly lower and remain there for hours. If you’re REALLY concerned about them, move them. Otherwise, I’d think they should be fine. Good luck!


Thank you very much!

You’re welcome! Also, from what I’ve read, many Hybrid Teas are sufficiently hardy to withstand long periods down to nearly 25F with minimal damage. Not “all”, but many and floribundas have long tended to be a bit hardier, in general. I’m grateful those conditions aren’t the norm where I’ve always grown roses!

1 Like

My “true hardy species” seedlings popped their head out of the ground in back north facing gardens, and one true 1st leaflet, between April 30th (nothing showing) and June 1st 2022.

Zone4a Cdn and not uncommon for snow falls at end of May.

Their smart as time encoded no doubt.

If spacing allows and if forecast concern, you could consider popping a small clear plastic cup over them with a small top vent hole in case sun comes out. I use vented cloches in spring for real tenders.

Daffies out in Feb aren’t they?

1 Like

My climate (Cfa according to the Koppen classification, average temperature in January 2.5°C) is very different from what people in America usually experience, as the minimum temperature we register during the year is typically just few degrees below 0°C (a couple nights at -6/-7), but we routinely get below the freezing point most of the nights in the Nov-Feb period; we do not have extreme cold peaks.

In the past four years, I’ve usually kept my seedlings in the fridge until when I have time to plant them all (usually the end of December), and then sown them directly outside. Most of my seedlings (mostly Austin’s, Kordes and Tantau’s moderns) have been routinely exposed to below-freezing temperatures basically every night with no evident negative effects. Of course, they won’t grow much until it gets a bit warmer, but no real issues.

I would suggest you shield them from snow and rain, though, if your area is wet and cold during the days. I keep them covered, as low evaporation due to low daily highs + high athmospherical humidity would keep the soil sogged. I’ll also have to set up some kind of netting in spring: last year we had a totally out of season hailstorm in march, when my seedlings were at the two/three leaves stage and basically lost the whole batch