The important thing to understand about tomatoes is they’re a warmth-loving plant *but* only within certain temperatures. Too cold and they have one set of problems, too hot and they get another.
The temperatures listed below are optimum for your plants and you can control or modify the growing conditions by:
- Warming up the soil in the early spring with clear plastic (but remove it before planting)
- Warming up the soil in the early spring with black plastic (not as quick as the clear but you can leave it on almost all summer)
- Using a frost fabric to protect tender young plants from cold winds and too-cool nights.
For Seedlings and Garden
Optimum daytime temperature for tomatoes is 70-82F
Optimum night temperatures 62-64 F.
Below 60F nutrient deficiencies may occur
Tomato ‘Yellow Mortgage Lifter’
For Garden Only
- A few nights of 56-58 F will cause rough fruits
- Over 86F, lycopene (what makes a tomato red) no longer develops.
- If night temperatures drop below 55°F, pollen won’t develop and flowers that open the following morning will not set fruit. An alternative damage is they will set fruit but that fruit will develop blossom end rot.
- If the day temperature reaches 90°F by 10 a.m., blossoms that opened that morning will abort. Or they’ll produce blossom end rot
The scientific explanation of some of your tomato problems has to do with the day-night temperature fluctuations. For example,if the night temperature drops below 50°F at 10 p.m. only warms back up at 8 a.m. the next day, the tomato behaves as if it were still night. It continues nighttime activities during daylight hours. But it also starts the daytime growth and you have a competition within the plant.
The daytime eventually “wins” but cold nights confuse tomato plants. Anything you can do to keep them warm and above 50F is a good thing. This means tossing some sheets over them or growing them under frost fabric until nights are warmer.
Here are all the organic vegetable gardening tips in one spot.