help with temp control

landarch 3/20/2013, 2:18 pm

I moved some tomato seedlings outside today and covered them with some heavy duty plastic (scavenged from a construction site dumpster). My outside temp is 38F and when I cover with plastic, the temp immediately goes up to 80+. I've pulled the plastic back a bit to let some of the heat escape...but what is the prime temp (or range) I should be shooting for?

The seedlings have been under natural sunlight since germination...I've not really had to use a grow light a whole lot because it ws really warm before this cold front moved in.

plantoid 3/20/2013, 2:58 pm

If I recall correctly ....

Tomato seedlings don't last long if the temp is much below 50 o F , evidently 55 o F of is the better survival zone for over night temps .
Much above 90 o F , they wilt and or get very stressed and prone to disease.

Hardcoir 3/20/2013, 3:06 pm

Your humid 80-degree temperature could not be more ideal. Tomatoes love that climate. Our greenhouse stays around 77-78 degrees with 57-65% humidity.

Come to think of it, that temperature is perfect for me too.

landarch 3/20/2013, 3:34 pm

great, thanks for the info..sounds like they'll be in good shape as long as move them inside as soon as the sun goes down.

After seeing the temps, I may score some points with the wife if I build a small protected area wrapped in plastic just big enough for her lawn chair, a book and a glass of tea...don't think she would want to come back inside.

quiltbea 3/20/2013, 4:58 pm

landarch....Ask her if she'd like some company. I could stand a bit of heat and sunshine just now and the tea is a plus for me.

bwaynef 3/20/2013, 11:10 pm

plantoid wrote:If I recall correctly ....

Tomato seedlings don't last long if the temp is much below 50 o F , evidently 55 o F of is the better survival zone for over night temps .
Much above 90 o F , they wilt and or get very stressed and prone to disease.

Mine have been in the garage when the temps (outside) went into the mid-to-upper 30s and they're fine. When they're being given plenty of light and the temps are cold they tend to turn purple, but they'll grow out of that and be better for it (since cold treatment is supposed to accelerate the onset of fruiting. Granted, the cold treatment is recommended mid-40s to mid-50s ...but they're doing well with the temps they've been subjected to.)

I'm debating about bringing in the ones I've got in the garage since lows tonight are going to 28ºF. My indoor/outdoor thermometer's stopped working so I'm not sure if my garage will dip below freezing or not.

yolos 3/20/2013, 11:20 pm

Ah ha - so that is why my leaves are turning upside down and are purple. Temps are too low in the garage. I better go turn on a space heater for a little while. Gotta protect those babies.

**camprn** 3/21/2013, 6:12 am

yolos wrote:Ah ha - so that is why my leaves are turning upside down and are purple. Temps are too low in the garage. I better go turn on a space heater for a little while. Gotta protect those babies.

Purple leaves, depending upon the plant species, could also mean mineral deficiency or imbalanced pH resulting in poor nutrient uptake.

yolos 3/21/2013, 9:29 am

Camprn - The plants were tomatoes. Uppotted into MM about a week ago. I hope the MM will correct the problem.

plantoid 3/21/2013, 10:01 am

bwaynef wrote:
plantoid wrote:If I recall correctly ....

Tomato seedlings don't last long if the temp is much below 50 o F , evidently 55 o F of is the better survival zone for over night temps .
Much above 90 o F , they wilt and or get very stressed and prone to disease.

Mine have been in the garage when the temps (outside) went into the mid-to-upper 30s and they're fine. When they're being given plenty of light and the temps are cold they tend to turn purple, but they'll grow out of that and be better for it (since cold treatment is supposed to accelerate the onset of fruiting. Granted, the cold treatment is recommended mid-40s to mid-50s ...but they're doing well with the temps they've been subjected to.)

I'm debating about bringing in the ones I've got in the garage since lows tonight are going to 28ºF. My indoor/outdoor thermometer's stopped working so I'm not sure if my garage will dip below freezing or not.

So any idea of the internal temp of the garage after you brought the plants in ?

Pollinator 3/21/2013, 10:39 am

landarch wrote: I may score some points with the wife if I build a small protected area wrapped in plastic just big enough for her lawn chair, a book and a glass of tea...don't think she would want to come back inside.

That's why I love working in the greenhouse in early spring. I "bump up" all the young seedlings that were thickly planted in trays, into individual plug trays or cups. It's a slow, tedious job, but it helps make strong-stemmed plants and the sunshine on my back is nice. On partly sunny days, you can tell within seconds, the heat difference when a cloud moves in front of the sun.

I would encourage any one thinking of building a greenhouse to think not only of the space needed by plants, but also to have a workbench, a stool, and some drums of water (to even out day and night temperatures).

The last few days, it's been uncomfortably hot, so I've had to open things up and bring in a fan. But now, it looks like we are going back to a cold spell.

bwaynef 3/21/2013, 12:27 pm

camprn wrote:
yolos wrote:Ah ha - so that is why my leaves are turning upside down and are purple. Temps are too low in the garage. I better go turn on a space heater for a little while. Gotta protect those babies.
Purple leaves, depending upon the plant species, could also mean mineral deficiency or imbalanced pH resulting in poor nutrient uptake.

I believe the mineral deficiency is Fe, but I might have mixed it up w/ Mg. I think its likelier to say that a tomato seedling that's been grown in cool temps is likely purple because of the cool temps rather than a mineral deficiency.

yolos 3/21/2013, 1:17 pm

Okay, I have done some research on the purple tomato leaves. The leaves have turned upside down and only the bottom of the leaf is purple. It appears to be a phosphorous deficiency which can be caused by cool weather. (There can also be a problem if the ph is off) Apparently the cool weather can inhibit phosphorous uptake. Once the plants/soil warm up, the condition should correct itself. I will have to see what the temp gets to in the garage at night. There is an older thread somewhere on this forum that gave the best explanation.

landarch 3/21/2013, 4:46 pm

I mix a litle hardwood ash into my seedling mix to help with trace elements.

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