I am also in the same situation, need advise.

I have repotted tomato seedling from 72-cellflat to sams cups. Half of the replications are sitting in un-heated greenhouse and half are in indoor grow rack. Last night's low was 28 and next 10days lowest would be 35. Should I leave them in Greenhouse? -Chandra

I have half of my seedlings in the garage and half in the house.

Last night, when it hit 28 degrees, my husband LEFT THE GARAGE DOOR OPEN. ALL NIGHT. Like, the big door that you drive cars through.

This AM I was shocked to find them all still alive and hopefully unhurt in any way!

Toughen those wimps up! ;)

Jo

look who's telling me to toughen them up! ha!

dody :)

Dody,

You can leave them in the cold frame if it stays above freezing all night with the lid closed. Tomatoes can freeze at temperatures of 32 degrees and lower, although it generally takes about 2 hours exposure, in my experience, to kill the plants back to the ground. Less than two hours exposure may damage them and set them back, but generally won't kill them unless frost also occurs.

Frost is a different issue. Frost can damage plants and, if the conditions are right (or, maybe it would be more accurate to describe them as "wrong"), frost can form at 37 or 38 degrees. I've heard it can form at 39 degrees but haven't witnessed that personally. I have witnessed a killing frost at 37 or 38 degrees and see it here just about every year. So, always protect the tomato plants from the possibility of frost anytime temps are expected to go below 40 degrees.

Having said all the above, I don't like to expose tomato plants to too much air temperature below 40 degrees. Once they are exposed to cold air temps, their growth will slow down and stall with the result being they'll often set fruit much later than they would have if never exposed to those cool temps.

Currently my tomato plants are outside most of the day or all day (less time is spent outdoors on very windy days when the wind exceeds the upper 20s) and back inside either the garage (well-insulated) or sunporch at night. If the temperatures are expected to drop below 30 degrees, they come from the sunporch into the house, but I leave the big plants in the garage because it stays warmer.

One thing to understand about tomato plants is that while some limited cold exposure early in their life is good for them, too much is not and will stunt them. Since my goal is to harvest tomatoes as early as possible (I usually harvest the first tomatoes from the early container-grown tomato plants in late April and from the in-ground plants in late May), I avoid letting them be exposed to any temperatures cold enough to make them stunt or stall. That's my personal preference because the earlier I harvest, the greater the overall harvest will be. If you don't mind a later harvest or less fruit per plant, you don't have to be extra-cautious about exposing the plants to cold temperatures as long as you protect them from freeze damage and frost damage.

For anyone who's pretty new to raising tomatoes, you should know that hot temperatures shut down pollination and fertilization of the large tomatoes, with 'large' in this case being anything more than an oz. or two. Thus, it is advisable to get good early fruit set before the high temps begin negatively impacting pollenization and fertilization. The temperatures that impede pollination can vary but basically high temps 92 to 95 or higher will do the trick as will low temps above 72 or so. Having high humidity in combination with those temps is even worse. So, if prolonged exposure to cold temps stunts your plants or makes them stall, then by the time they get going again, they may not get good fruitset before the heat arrives. That's the main concern with too much cold exposure above and beyond the plants possibly freezing.

Dawn

well, that's what i needed to know! thank you for the info- i'll be bringing them in at night for awhile then. i don't mind one bit, and if it will help me get better fruit set, and then i'm all for it. after the dismal harvest i got from tomatoes last year, i'm doing my best to not repeat the same mistakes again.

i get to make all NEW mistakes this year! har-har-har!

jo, i hope my comment didn't come off as snarky, as it wasn't meant that way. i thought i remembered you being concerned about your baby plants in another thread...and i was just teasing you. :)

Well DANG! I thought DH was showing them some tough love. ;)

I'm gonna kick his butt when he gets home!!!!

Jo

PS Dody I never thought you were snarky, it made me laugh!!!

Jo