Great question and one I'm curious about too.
Do we keep the tops on if seeds have NOT sprouted? We're going to have high 70-80's this weekend and I'm not sure if they should come off. (all perennials)

What about tomato that haven't sprouted yet? top on/off?

I feel like a helicopter parent with my seedling "children" ...tops on.. tops off .. do they need a blanket .. which ones to blanket .. eeeek -- this is the hardest part to know!

If you are hovering and coddling then you have missed the whole point. The seeds germinate when they know it's generally safe. Perennials that are mostly sprouted, tops off and stay off. Hardy annuals, same thing.

THE ONLY plants i worry about I haven't sown yet - the tenders like zinnia, cosmos, marigolds etc. The ONLY herb I worry about is basil that has germinated when temps go lower than 40. OTHERWISE - nothing changes. My datura haven't sprouted yet or my 4:00s. Lid stays on. Dats are relatives of toms, so I imagine if i winter sowed them, they wouldn't be up either.

Hang loose. Year 2 is much less stress, i promise.

Thank you, Bakemom, you answered several questions that I too had. Now...how to fix the enlarged right eye that resulted from my peering into milk jugs for the last 6 weeks? (I would add an amusing little 'wink' symbol, but I do wink with my right eye!)

I'm with Nancy and Bakemom (Karen) on this too, once germinated unless freezes are expected leave the tops off. Now we have had temps of 70 degrees this past week, the next week its going to go into the 50's for day time highs, and in the 40's for night time lows. My basil has germinated and that is the only one I will leave the top on for, other than that one container...tops off if germinated, :)
and btw I'm an oldie with this, I started back in 2001.

Alberta

Agreed. Once tops are off, they stay off. If tender annuals have sprouted (which I haven't even planted yet) and frost threatens, throw a blanket over them. I'd keep tender plants in a group together, so if frost threatens you can get them all under one blanket--easy on easy off. Seeds which haven't sprouted yet need their tops to maintain relatively constant moisture for germination. Most seeds are laying on top of the dirt, so open tops allow breezes to dry them out, even if there is still moisture below in the container. Once sprouted, the roots are able to provide moisture to the sprout when the tops are off.

I've also been doing this more years than I remember.

Martha

I agree with the last 3 posters and want to emphasize this caveat- do NOT sow tender annuals until you are sure the temps will remain above freezing consistently.

I agree, not a concern for hardy annuals or hardy perennials. That's why they're called HARDY.

The only ones of concern are tender annuals and perennials. And frost doesn't magically happen at 32 degrees. Sometimes there will be no frost at 31, other times it can occur at 34. It's occurrence is a product of actual temp, presence of wind, level of humidity... This article isn't about wintersown plants, but it does explain well how factors affect frost formation. See link below.

I only worry about tender annuals. I cover those.

We're going to be at or near frost territory tomorrow night. I'll check the forecast tomorrow afternoon and decide if I might need to cover. I don't have that much faith in meteorologists that if they say low will be 35- I know they're often off by more than a degree or two.

Karen

Here is a link that might be useful: frost formation

I have tops off everything here including the unsprouted containers. It's been so warm here (high 70s to mid-80s) for an extended period that I am concerned about the seeds themselves cooking in the containers. It means I have to be vigilant about moisture levels, as the tops help keep moisture in. I have already planted out a bit, and if we get a snap freeze, I will lose some of what I can't cover (my tomatoes all have second or third leaves already) - and that might amount to a good bit.

My way of not getting bent out of shape, should this happen, is keeping a ridiculous number of seeds around. If I lost EVERYTHING, I could still start plenty more - and still have enough seeds for the next 5 years.

Karen,
thank you so much! The article about frost is fascinating. And it explains to me why - with the same temp - a clear night is colder than a cloudy nite. Never understood that. :)

going back to finish the article...

You're welcome. I too think it's a nice simple explanation without a bunch a scientific jargon.

Heads up- frost warning around here tonight.

Karen

Yes!
here too. Time to get the row covers out..

We're supposed to get a hard freeze tonight in Zone 6. The weather man is calling for a low of 25 over the next two nights. My sprouted containers are on shelves on an open porch. I intended to replace tops and throw a blanket over the whole set up. Will this be enough?

Sorry, newbie nervousness here. I realize I'm not supposed to coddle my sprouts, but I just want to make sure that a blanket is going to be enough protection for 25 degrees. I had no intention of adding heat, but I would move them to the garage if needed . . . (All my sprouts are hardy perennials, but none of them have true leaves yet, if that makes a difference.)

Ok, i'm the dufus that sowed zinnias too early and they are about an inch tall already. I didn't cover them with the freeze 2 days ago because i was out of town, darn! They looked ok yrdy so fingers crossed! Covered everything with blankets last night. Thx for all the guidance for us newbies you guys!!

I am a newbie, and was just logging in to report potential panic on my tomatoes. I have eight jugs of tomatoes that I winter sowed. From the WS database, it looked like it was ok for tomatoes to over winter (rather than sow in April). They all germinated and as of yesterday I had seedlings that were showing true leaves and were two inches tall.

I've been sick the last few days and a little out of it, so I forgot that our temps were supposed to get down around 37 degrees, and I would have covered the jug tops back up but I was too sick and tired and I forgot. This morning about half of the tomato seedlings look fine, hale and robust as ever. But the other half of the varieties seemed much more affected. The romas are all droopy and sad looking, like they just ran a marathon.

Fared best: Stupice, Roma, Yellow Pear, Black from Tula
Fared the worst: Striped Roma, Brandywine

Jury's out on how the green zebra and chocolate cherry toms are doing, as they were littler sprouts to begin with.

It seems there may have been some wind effect, as even within the same jug some of them (planted closer to one wall) fared better than others.

Thats my evidence, for what its worth. Think they'll bounce back?

Essence of time will tell, but probably. If the low was 37 and the air was moving, I imagine they'll be OK.

It got down to 34� last night, some breeze. I don't think we actually got frost.

Karen

The soil in my containers was frozen when I got home from work this morning. The ones that have sprouted look all right, although there is one container of Scabiosa that darkened in color. Is this temporary? We're supposed to be cold at night all week, but not quite as cold as last night. Mother nature is having some serious mood swings. I hope everyone makes out okay through all this crazy up and down weather.

Ok, i'm the dufus that sowed zinnias too early and they are about an inch tall already. I didn't cover them with the freeze 2 days ago because i was out of town, darn! They looked ok yrdy so fingers crossed! Covered everything with blankets last night. Thx for all the guidance for us newbies you guys!!

Ok, i'm the dufus that sowed zinnias too early and they are about an inch tall already. I didn't cover them with the freeze 2 days ago because i was out of town, darn! They looked ok yrdy so fingers crossed! Covered everything with blankets last night. Thx for all the guidance for us newbies you guys!!

Oops, sorry!