Running lights overnight during cold treatment

[Csross]

For the past few years, I've just started a few seeds under a desk lamp in front of a sunny window. Thanks to all of you enablers, though, I'm now starting a bunch of different varieties of tomatoes and other vegetables for everyone I know, and I've run out of space. So I'm looking to move my setup into the garage under florescent shop lights, and I've got a question about temperatures.

Last night it got down to 36F outside, but the shelf in my garage where I want to start seeds is on an interior wall and only went down to 48F. Based on what I’ve read, that still seems ok. I was thinking, though, since there’s no natural light in there, I could run the lights overnight and have them dark during the day, which would keep them a bit warmer and give me a little cushion if we get another colder night. Would that screw up their ‘diurnal rhythm,’ or isn’t that a concern with plants? I’ve got a timer and was planning on running the lights for 14 hours per day. (Just regular Home Depot florescents, 6500K, 2700 lumens)

Right now, the tomato plants have the cotyledons fully unfurled, but haven’t started their first true leaves yet. The lettuce, bok choi, etc, were started earlier and have their first true leaves out. The garage will probably get down to 46F at night, up to 60+F during day depending on weather. I’ve read that cold treatment should last 2 weeks, but I assume that’s a minimum? I plan on leaving them there until I start hardening them off for planting. Plant out is generally in early May, but I’m hopeful it’ll be a bit earlier this year due to the warm spring we’ve been having.

Does running the lights overnight make sense? Anything else I need to be doing? Thanks!
-Chris

[PaulF]

My opinion is they need a little more heat. A heat mat most likely would do the trick. As for the timing of the lights being on, I don't think it matters whether it is daytime or nighttime. My lights are on 16 hours/day. Using fluorescents will not really do much for temperature increase since they are a relatively cool light source.

Planting outside for me depends on the plants rather than the outside temperature. If the plants are ready to transplant when the weather is right, in the dirt they go. If the weather is right and the seedlings are not, no planting.

[Dewayne mater]

I run my lights about 16 hours a day and do make sure it is overnight and into the morning, when it is coolest in my garage. Cool temps for plants will definitely slow the growth. Mine typically take 2 months from seed to plant out and folks that work in warmer temps consistently have shorter times to get plants to a good transplant size. If you have a gradual warming in the Spring, I think that your temps are fine. If it stays near those temps consistently, that is probably a bit too cool.

[Csross]

Thanks for the replies. I left the lights on overnight last night, and though it got down to 40F outside, a thermometer next to the plants was reading 55F at 6:30 this morning. I'll keep an eye on them, obviously, but I think we're in business!

[Worth1]

I was waiting for good replies and you got some.
Here are my observations.
If the plants are in the cold during the time they are collecting energy from light.
They will grow in the dark IF the soil gets warm enough.
Your situation was to keep them in the cold all of the time.
At the temperatures you are describing they will be more or less be in a holding pattern until they warm up

Worth

[Csross]

Thanks Worth. I thought the point of cold treatment was to intentionally stunt them, so that they'd produce stockier stems and start fruiting earlier? So I wasn't expecting them to grow much over the first two weeks of being in the garage. Temps seem to be running from 55F - 65F depending on the outside temperature. What temperature range do they need to be held at consistently in order to grow well? I assume that my garage temperatures will gradually increase over the next month, but I'm afraid a heating pad will warm them too much.

[oakley]

Space is an issue when potting up. Going through that right now.
I've been running my LED's 24/7 and dancing trays around. Other shop lights 16 hours.

I would keep your tomatoes under lights where they are, and try to keep them there
once potted up for a week. After strong growth tight to the lights 1-2 inches, then your
garage set-up should be a better temp. It seems to be warming up where you are.
(my parents live in the area though may be warmer DelMarVa)

My grow room is 60-64 and just cool enough for nice slow growth and thick stems.

[bower]

My cold treatment area is an unheated window with a shoplight hung above them. Nighttime temp certainly goes to 50, and anything 50 and above should be fine for night. Daytime would hit 60 to 65 this time of year. And the lights, although fluorescent, they do give off enough heat to be noticeable right next to the seedlings in a room with no other heat source.

The only concern I would have about flipping day for night, you do want them to be colder at night than in the day. They need 8 hours of darkness and the natural cooling cycle is the best. OTOH if you monitor your temperature, that may work out fine with the flip at least until it starts to warm up.

As regards the slower growth, this is true for sure, but last year I experimented with growing them up in a warmer room upstairs, that would have nights around 60 + and days 65-70 or more - sometimes shooting up a lot if the sun decided to shine.. They grew way too fast. I'm back to the basement.

[KarenO]

If I live to be a 100, I will never purposefully stunt a tomato plant.

This "northern Gardner" says if you need to slow the growth down, they were planted too early.
For my purposes, I plant my seeds and do everything I can to maximise as rapid and vigorous growth as I can so that the plants "hit the ground running" right from the get-go with as large as I can manage and already blooming plants ready for the garden at the right time (well after danger of frost) . Having a greenhouse or the dedication to bring plants in and out and the space to pot up to litre + pots is required for my method but I always had ripe tomatoes in the middle of july in a Zone 3 outdoor garden. I have never pinched a blossom in my gardening life either.
I believe that Tomato seedlings want to grow fast and they do better if you let them and help them. I think more focus should be on sowing at the right time and not sowing more than can be managed with good light, watering, fertilizer and warmth. In particular in a short season garden I observe gardeners struggling using the same technique and timing as our southerly neighbors and it is causing more problems than it solves I think.
My Northerly perspective for what it's worth
KarenO who doesn't believe in "cold treatment", not fertilizing seedlings , blossom pinching, small seedling cups, DE, or under watering of tomato seedlings. I am Not trying to start an argument but there is more than one way to do things and if gardeners are having trouble, try something different next year .

[Jimbotomateo]

Originally Posted by KarenO

If I live to be a 100, I will never purposefully stunt a tomato plant.

This "northern Gardner" says if you need to slow the growth down, they were planted too early.
For my purposes, I plant my seeds and do everything I can to maximise as rapid and vigorous growth as I can so that the plants "hit the ground running" right from the get-go with as large as I can manage and already blooming plants ready for the garden at the right time (well after danger of frost) . Having a greenhouse or the dedication to bring plants in and out and the space to pot up to litre + pots is required for my method but I always had ripe tomatoes in the middle of july in a Zone 3 outdoor garden. I have never pinched a blossom in my gardening life either.
I believe that Tomato seedlings want to grow fast and they do better if you let them and help them. I think more focus should be on sowing at the right time and not sowing more than can be managed with good light, watering, fertilizer and warmth. In particular in a short season garden I observe gardeners struggling using the same technique and timing as our southerly neighbors and it is causing more problems than it solves I think.
My Northerly perspective for what it's worth
KarenO who doesn't believe in "cold treatment", not fertilizing seedlings , blossom pinching, small seedling cups, DE, or under watering of tomato seedlings. I am Not trying to start an argument but there is more than one way to do things and if gardeners are having trouble, try something different next year .

Thanks KarenO. That answered a zillion questions in one shot! . Jimbo

[Dewayne mater]

Many of us have a defacto "cold treatment" by the fact that where the young plants are growing, it is cool and too expensive or impractical to heat their area to ideal growth temps - probably in the 70s.
I fertilize small plants using a weak solution of Texas tomato food, usually on every other watering. The temps where they grow warm up as the outdoor temps warm up and when that happens, naturally, the growth rate accelerates. I also believe in letting the soil dry out because I don't think any tomato likes to be wet all the time and if they are, you encourage fungi to grow.

I'd say there is very likely more than one way to do raise seedlings that works very well. The key you want is plants big enough and with thick enough stalks to handle it when you put them outside where they are sure to face cool temps and high winds for a while - at least in my neck of the woods. So, since it hasn't been said here, I highly encourage the use of a fan to blow on the small plants. Gently at first and with increasing speeds as they get bigger and stronger. This encourages thick stalks.

[bower]

'Stunting' is a harsh word.
The main point of cold treatment is to activate gene expression for cold tolerance. KarenO doesn't need it because of her methods, potting up into large pots and planting out when it's really warm. Those plants didn't even know they were in Edmonton.

OTOH where I live it's never really guaranteed to be warm. I don't have the space to pot up and keep them indoors until July, so they will have to be planted in the greenhouse out of beer cups, and nights will be lower than 50 F on times, 50 being the benchmark for "good night". So my seedlings need to grow proportionate to the small pots they are allowed, not too tall, and they need to be ready to put up with a lot of miserable weather!

[KarenO]

Cold nights are a given and 50 degrees is normal. My objection is to purposefully stunting plants , to "slow them down". "cold treatment" implies purposeful stunting imo not normal night time spring temps.


KarenO

[Worth1]

I don't think I have ever stunted a plant and n my life.
My methods will not work up north.
Worth

[Csross]

Wow, thanks for all the input! Sorry, "stunting" was the wrong, inexact word. As I said, I've previously only started tomatoes in my warm dining room, where they never experience any temps below ~64F, so I was concerned about moving them to the garage. Then I saw Amideutch's thread on cold treatment here, and started reading about the benefits of exposing them to colder temperatures while they're still young. "Basically this cold treatment is used to give healthier, more stocky seedlings that will give increased yields and earlier harvests." That's the line that caught my eye. In that thread, that's defined as 52-56F overnight for 2-3 weeks, and then warmer.

I'm not trying to slow their growth, they just got their first true leaves and I hope to plant out in a month or less, depending on weather. I wanted to make sure that some cold (i.e. 48-50F) wouldn't hurt them at this stage, and from your responses it sounds like they'll be fine. Based on the forecast, I'm expecting their overnight temps will be in the mid to low 50s for this week.

Bower, thanks for the advice on switching the diurnal cycle. I'll probably keep it like this for a bit longer, and then as the overnight lows warm up, I'll switch it back to normal.

I'm glad to hear that there are many different techniques for successfully starting plants! Thanks everyone.