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  • Minimum temp for tomatoes

    What is the minimum temperature for tomato plants? I am wondering when I can place them into my greenhouse.

  • #2
    I am not sure what minimum temp they can survive with, but have always been told they will not grow/thrive under 70 degree soil temperature.


    • #3
      they need warmth to sprout and grow, but will survive anything above freezing. Kind of a tapering off thing. the lower the temp below 70 the slower the growth, or longer it takes to sprout.


      • #4
        As long as they don't freeze, they'll survive (unless fungus attacks them).

        I picked my first tomatoes a couple weeks ago, from a volunteer that appeared just before winter. This is zone 9-10, and it got to 34-35 F a couple times. It's in a protected place so it's warm if sunny.


        • #5
          In air temperature greater than 35-40 degrees F, they should survive (maybe only a few days at those temps). Soil temperature below 70 degrees, plants will survive but will"spin their wheels" and not thrive as well as those planted in warmer soil. Tomatoes put out in soils less than 70 degrees may be stunted, have less productivity and be more susceptible to disease later on because of their initial weakened start.


          • #6
            I start them indoors on a heat mat and transfer to my greenhouse. It is tricky to decide when they should go into the greenhouse. After the first true leaves? After the initial germination?


            • #7
              120F = 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.

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

              70F to 92F = 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.

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

              50F to 65F = 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.

              32F to 50F = 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.

              28F to 32F = 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.

              22F to 28F = 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.

              15F to 22F = 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.

              0F to 15F = 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 60F, 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 45F then the greenhouse must be let rise to a high temp near 100F the next day. If this is done, then the plants totally reverse all effects of being too cold the night before.



              • #8
                Dar, thanks for this information. I have copied and pasted it into a word doc so I can have it for future reference!


                • #9
                  This is useful information, thanks. I'm thinking about starting my tomatoes one week later than I usually do this year. That way, I can transfer them into the greenhouse right after germination and not do any grow lights in the house. But I will monitor the temps in my greenhouse the week before and see how things are coming.