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Old March 2, 2017   #16
Jimbotomateo
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Thanks Mark! My question was simple . Your answer was as interesting and informative as anything I've read in a very long time. One thing I found strange is your nite temps are close to what we experience. We're seldom over 60 here at nite. Thanks for the tips! Jimbo
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Old March 2, 2017   #17
sjamesNorway
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The following is the best guide I've found about temperatures for growing tomatoes, first posted by Fusion_power here:


Tomato Temperatures(fusion_power)

120°F = Severe heat, but if plenty of water is available, the plants are fine. This temp is way above levels at which pollination can take place. Plants with heavy fruit set may show stress. Nutrient transfer imbalances occur because the plant is busy moving water into leaves instead of moving nutrients into fruit.

92°F = This is the temp at which pollen starts clumping and blossoms begin to drop.

70°F (21C) to 92°F (33C) = This is the goldilocks zone. Tomatoes grow prolifically, flowers set readily, plants need maximum fertility in the soil. The high end of this range is optimum for spread of several foliage diseases.

65°F (18C) to 72°F (22C) = the best temperature to grow seedlings. Temperature can be used to slow down growth. 60°F will cause growth to be reduced about 1/4 compared to 70°F.

50°F (10C) to 65°F (18C) = this is the beginning of cold stress. Tomato plants in this range grow slowly, often produce anthcyanins (turn purple), and become pale green from loss of chlorophyll function.

32°F to 50°F = This is the range where normal tomato plants show severe cold stress. Leaves shrivel, turn yellow, wilt, stems lose turgor, roots stop absorbing water. Rubisco is deactivated by free radicals with byproducts accumulating which causes the leaves to die.

28°F to 32°F = This is the maximum range most tomatoes can withstand without freezing. Note that if frost forms on the leaves, then the leaves will freeze and die. The plant may live and can form new leaves, but the stunting effects take quite a bit of time to overcome.The time a plant can stand at this temperature is very short, in the range of about 6 hours in a 7 day period. If the temperature remains below 50 deg F on average and if the temperature dips below freezing a couple of times, the plants will deteriorate rapidly.

22°F to 28°F = This is the range that a few select varieties can withstand for brief periods of time but stipulating that frost on the leaves will still kill them.

15°F to 22°F = This is the range that a few Russian cultivars are reported to survive, again only if frost does not form. The reports I have read indicate that this tolerance is only for a limited time period, in other words, repeated low temps for 3 days or more will still kill the plants.

0°F to 15°F = A few Russian cultivars are able to handle temps this low for brief periods of time. This is the low end of the range that wild tomato species S. Habrochaites, S. Chilense, and S. Lycopersicoides can withstand.

As the temperature goes below 60°F, tomato plants enter a state where normal photosynthesis ceases. Sugar accumulates in the leaves, rubisco - a crucial chemical in the plant- begins to be deactivated by free radicles. This process causes the leaves to become dysfunctional in such a way that they can not recover. One very special trick that greenhouse growers MUST know is that if plants are exposed to overnight lows below 45°F then the greenhouse must be let rise to a high temp near 100°F the next day. If this is done, then the plants totally reverse all effects of being too cold the night before.

DarJones
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Old March 12, 2018   #18
HeatherBell
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Default Moving from lights to Greenhouse

I started my seedlings inside this year under lights because last year I had to start them so late in the greenhouse to keep temps warm enough to germinate. My question is this. I am in Southern Ohio 6b, and I would like to move my six inch tomato plants into the greenhouse because I am running out of room! Do I need to harden them off? and will the low temps at night be okay as long as it doesn't dip below freezing? The greenhouse has had average low temps 30's and average high temps 90's. And how cold is to cold? Thanks for any advice! -Heather
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Old March 12, 2018   #19
bower
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sjN, thanks for reposting that guideline from Fusion - my favorite too.
I have closely observed plants at daytime highs not reaching 60 F, and it would be rare to see any evidence of leaf growth, opening of flowers, or setting of fruit. OTOH many cool tolerant varieties will grow, flower and set and grow fruit just fine at any point between 60 and 70 F. Some other varieties really don't do much fruit growth unless highs are 70 F or above, and the nighttime lows of 60 F make a big difference for them as well. I started paying attention to the 60 F night after AKMark mentioned it, and I do think it has a marked effect on the rate of fruit growth and ripening across the board.
I used to consider 48 F as the nighttime low where I should protect the young plants. However being a bit more careless I found that plants showed no stress with nights down to 45 F, as long as the soil wasn't too wet, foliage also dry, and were not suffering additional stress ie from just being transplanted.
Fusion's advice about transplanting when you have a couple of warm days forecast was the best ever. The plants get comfortable in 2-3 warm days, and are then able to handle some cool temperature stress without showing it.
Also the research which Vladimir brought forward, about cold tolerance being better when dry vs wet has also proved correct for me - I did some experiments on 'extra' seedlings that were outdoors, and sailed through the cold nights with no damage if I didn't water them, vs. those that I watered were a mess of dead and fungally infected leaves after the same night.

Since my greenhouse isn't heated, I aim for night lows of 50 F as optimal for putting out seedlings or young plants. Warmer is fine, but anything below 45 F, is getting into the danger zone and I will cover them to prevent going lower than that. I will often open the vents if daytime temps get above 70 F, try to keep it around 70 -75 F and will close if it drops below 65 F.
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Old March 12, 2018   #20
Cole_Robbie
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Quote:
Originally Posted by HeatherBell View Post
I started my seedlings inside this year under lights because last year I had to start them so late in the greenhouse to keep temps warm enough to germinate. My question is this. I am in Southern Ohio 6b, and I would like to move my six inch tomato plants into the greenhouse because I am running out of room! Do I need to harden them off? and will the low temps at night be okay as long as it doesn't dip below freezing? The greenhouse has had average low temps 30's and average high temps 90's. And how cold is to cold? Thanks for any advice! -Heather
If they have never been outside, the sun will burn off all the leaves and the plant will start over with new leaves. Most of hardening off is UV light tolerance. Artificial light bulbs don't make the UV spectrum, because it gives people cancer. Start gently with the sun. A cloudy day is probably ok. If it is sunny, I would put them in the shade.

As far as what low temps are too low, my plants tend to get sick when they get below 40 or so. 60 is probably best as a minimum low. I have been covering plants with hoops over then benches and a small heater underneath. My weather has been cold, but most of my stuff looks ok so far.
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Old March 12, 2018   #21
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Just looked up 'cardinal temperatures' as Nematode's link didn't work for me. Here's what the scientists say about it. So far I'm baffled about the low 'base temperature's they reported..still reading..
http://hortsci.ashspublications.org/...47/8/1038.full
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Old March 12, 2018   #22
HeatherBell
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Originally Posted by Cole_Robbie View Post
If they have never been outside, the sun will burn off all the leaves and the plant will start over with new leaves. Most of hardening off is UV light tolerance. Artificial light bulbs don't make the UV spectrum, because it gives people cancer. Start gently with the sun. A cloudy day is probably ok. If it is sunny, I would put them in the shade.

As far as what low temps are too low, my plants tend to get sick when they get below 40 or so. 60 is probably best as a minimum low. I have been covering plants with hoops over then benches and a small heater underneath. My weather has been cold, but most of my stuff looks ok so far.

I thought maybe this would be the case. I was hoping for something with a little less transition. I may just have to make more room for other plants and start the hardening off in April. Thanks for the help!
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Old March 12, 2018   #23
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Right now my seedings get 65 to 70f inside, 24/7. When I start hardening off they get 65 during day and about 45 at might (in the garage). That sort of mimics outdoor weather right after plant out. It works ok for me.
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Old March 13, 2018   #24
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I thought maybe this would be the case. I was hoping for something with a little less transition. I may just have to make more room for other plants and start the hardening off in April. Thanks for the help!
you can move them out if it is warm enough... just lay a sheet of floating row cover ( or a cheap white sheet- try goodwill for a few disposables if you have one close)over them to shield them from direct sun. I planted up my hanging baskets because it needed done even though the plants weren't quite hardened off yet. I suspended floating row cover over them just to give them a bit of shade. it works well. today I will put the hangers on my other baskets I planted up yesterday afternoon and do the same... I planted up fuchsias and they need shade and I don't have any on the house yet.
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Old March 13, 2018   #25
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Here's some tomato temperature trivia from the paper I linked above.

Photosynthesis:
"In a study conducted by Ogweno et al. (2009), detached tomato leaves were exposed to 15, 25, and 35 °C for 5 d. Leaves at 15 °C exhibited similar photosynthetic rate as those at 25 °C, whereas leaves at 35 °C had significantly lower net CO2 assimilation rates
Low temperatures of 4 and 6 °C were found to dramatically reduce photosynthesis of tomato plants (Byrd et al., 1995), whereas at 1 °C, photosynthesis of tomato leaves ceased
There is also a minimum night temperature effect in the model that reduces the next day’s leaf photosynthesis, which concurs with reported reductions in photosynthesis of tomato when the minimum temperature (Tmin; night temperature) is below 10 °C .." 10 C = 50 F.
4-6 C = 39-43 F.

Fruit set:
"The optimal range reported for fruit setting in tomato is reported to be 15 to 20 °C (Went, 1945) and 18 to 20 °C (De Koning, 1994). Fruit set is low at both low and excessively high temperatures." 15 C = 59 F, 20 C = 68 F.

Vegetative growth:
The internode length growth shows a marked linear response to temperature,...over a 10-d period at 16, 20, 24, and 28 °C average (over NT and DT) air temperatures showed that the corresponding lengths reached by the internodes were 12, 18, 27, and 30 mm, respectively...
Topt1 for stem elongation and leaf expansion (specific leaf area) is 26 °C (close to Langton and Cockshull, 1997-28C).

Fruit growth:
"According to De Koning (2000), temperature appears to be a principal factor determining the duration of the tomato fruit growth period. His results showed this period to be 73 d at 17 °C (63F) and 42 d at 26 °C (79 F).
High temperature shortened the growth period during two phases, first during the young developmental phrase and again close to maturity when temperature had a great impact on days to harvest. The middle phase of fruit growth was less sensitive to temperature. "

Crop life cycle to maturity:
"....We then simulated a range of temperatures by steps of 3 °C using fixed temperature regimes of 20/10, 23/13, 26/16, 29/19, 32/22, 35/25, and 38/28 °C Tmax and Tmin, maintaining the Tmax and Tmin differentials. Crop life cycle to maturity was shortest at the 29/19 and 32/22 °C, being particularly longer at the coolest temperatures .." (29/19 C = 84/66 F)

Fruit size and yield:
"A long growth period was a significant contributor to greater fruit yield and higher biomass that occurred at cooler temperature, .....Simulated fruit size (average at maturity) was largest at coolest temperature (15 °C) and was reduced progressively as temperature increased...
Adams et al. (2001) found that fruit size was largest at 18 °C and declined as temperature increased, because the effect of shorter fruit growth duration dominated the effect of a higher optimum temperature for fruit growth rate. ..De Koning (1996), likewise, found largest fruits at 17 °C, decreasing to 23 °C." 17C = 63 F.
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Old March 13, 2018   #26
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"Adams et al. (2001) found that fruit size was largest at 18 °C and declined as temperature increased, because the effect of shorter fruit growth duration dominated the effect of a higher optimum temperature for fruit growth rate. ..De Koning (1996), likewise, found largest fruits at 17 °C, decreasing to 23 °C." 17C = 63 F."

Really? Biggest fruit at 63F? Do the grow-for-size people know this, or concur with this?

Nan
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Old March 13, 2018   #27
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Quote:
Originally Posted by Nan_PA_6b View Post
"Adams et al. (2001) found that fruit size was largest at 18 °C and declined as temperature increased, because the effect of shorter fruit growth duration dominated the effect of a higher optimum temperature for fruit growth rate. ..De Koning (1996), likewise, found largest fruits at 17 °C, decreasing to 23 °C." 17C = 63 F."

Really? Biggest fruit at 63F? Do the grow-for-size people know this, or concur with this?

Nan
It was news to me, but I'm sure the grow-for-size people know all the science and then some.
These experiments are interesting but may be hard to map onto a reality where we don't actually control the temperature, and instead are living with the seasonal changes and whatever ups and downs the weather may bring..

I almost always get bigger fruit outdoors here (plenty colder, and plenty later as well!). I thought it was because of bees and wind making a difference in pollination but maybe not so.
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Old March 13, 2018   #28
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Just wanted to add to point out that the research was done using a couple of standard commercial varieties. In my experience there is a huge variation in temperature tolerance within the tomato genome. So your mileage may vary... quite a lot.
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