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Vegetable Gardening

50 degrees F for tomato seedlings

11 years ago

My tomatoes and peppers are up and growing well. But this cold snap has me in a quandry. I use my sunporch as a greenhouse, where they can get natural light plus the grow light. But it's down to 50 out there now, and likely to go lower at night.

I'm suspecting this is too chilly for them. I could bring them inside the house, where they won't get the natural sunlight. Or I could stick the heated seed-starting mat under them.

What's the optimum temperature for young solanaceae seedlings? And how low can it get before it's going to slow them down?

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Comments (6)

ruthieg__tx
11 years ago
Well 50 ins't optimal but as long as it isn't freezing I am not bringing mine in...It was 43 here last night and mine are mine...One year they were out and we had a sudden cold spell so I ran out and covered every thing. All but one did just fine and while they didn't seem to be doing all that great in the cooler temp weather....when I pulled up the one with the burned growing tip, I was shocked at the size of the root ball since it had only been in the grown maybe 2 and a half weeks...so if if they slow a little you will still get a good start on the season and I think that is important... No longer than they will have to be out there in the cold they probably will be fine...
digdirt2
11 years ago
I only worry if it gets below 45. That's when the heaters are set to come on.

Dave
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Hello all - thanks for the responses! Yes - I can turn off the lights for germination and still maintain a temperature of at least 75 I believe. Lights on - I've got a 20 inch area front to back on wooden shelves. (solid shelves, no slats or anything for the heat to rise and escape.) I tried 2 lights - but if I have those 2 inces above the trays / seedlings - then some are missing out on lights (With trays oriented long way front to back.) So I figured I could squeeze 2 more shop light fixtures in there. So - 4 shop light fixtures , total of 8 bulbs, 4 cool, 4 warm. I could maybe take a bulb out of each fixture to start when the seedlings are still very small?? then add the bulbs once I can get the lights up a bit. It's a tight space to begin with. What would you suggest as maximum ambient air temp right above / around the plants? Thanks all! Jon
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User
Original Author
11 years ago
I can keep them above 45.
NilaJones
11 years ago
That's my experience, too -- they might not show any growth above ground, but they will make wonderful roots.
fusion_power
11 years ago
Tomatoes should be kept above 50 degrees, but there is a trick that can help if they get colder. Say your tomatoes go down to 35 degrees overnight and sit at that temp for 6 hours. The next day, put them in a greenhouse and let them get up above 90 degrees for 6 hours. Each hour above 90 degrees counters an hour spent below 50 degrees.

Why is this so?

When a tomato gets cold, Rubisco - a chemical vital to plant growth - is deactivated. Letting the plant get above 90 degrees the next day reverses the effect. I use this trick to very good effect in my greenhouse. It allows me to deliberately cold stress my tomato plants and then reverse the effects the next day.

So you don't have a greenhouse? Well, you can make do with a plastic tent or even a partially covered aquarium. Don't EVER put seedlings in a fully closed aquarium, the temperature can easily get above 200 degrees in full sun. A gap an inch wide at one end is usually enough to bring the temp down below 120 degrees which is safe for tomatoes. Be sure to water them well, seedlings will consume incredible amounts of water when in direct sun.

DarJones
jonfrum
11 years ago
Can you give us a citation for the deactivation of Rubisco at low temps? I just did a quick search, and the literature I found only talks about the inactivation of Rubisco at HIGH temperatures.

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