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Is It Too Hot for Tomatoes?

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Soaring temperatures in midsummer can lead tomato gardeners to ask if it's too hot for tomatoes.

Even though tomatoes are the classic summer plant, it’s natural for gardeners to think they suffer when temperatures are too hot. (Everything else is drooping!) What should you do for your tomatoes during a heat wave? How much is too much heat and sun?

Here’s the dirt on whether or not it’s too hot for your tomatoes … and what to do about it.

Will extreme heat kill my tomato plants?

To put your mind at ease right out the gate, let’s answer this important question. No, a heat wave will not likely be fatal for your tomato plants, especially if you can keep them watered. (Read more about best tomato watering techniques.)

Here’s another piece of good news: tomato fruit already on the vine and ripening will likely be OK when it’s super hot outside. Intense sun can make fruit more vulnerable to sunscald, but they can survive and thrive with a bit of shading.

It’s the tomato blossoms that suffer most during a extreme heat. Read on.

So what's the downside in really hot weather?

Stress, stress, stress. Daytime temperatures consistently above 90° F or night time temperatures consistently above 75° F create all kinds of stress for tomato plants. It’s too hot for tomatoes to be pollinated. That means fewer fruit.

But even more worrisome is the toll the heat takes on the plants. Heat stress forces a plant to increase transpiration (pumping water through its system) to survive, especially when the heat continues for prolonged periods. Heat stress not only slows down your plant’s progress in producing, but it also makes your plant more vulnerable to diseases and pests.

A heat wave means …

• tomato blossoms won’t open
• pollen is destroyed
• no new fruit will set until normal temperatures resume
• leaves curl
• plants concentrate on simply surviving

What can you do to prevent this kind of tomato stress … or at least reduce it?

1. Plant smart

Figure out the best place to plant your tomatoes … and it may not be what you think.

Tomatoes seed and seedling packet labels tell us to plant in “full sun.” That means different things in different geographic areas and as seasons change.

What exactly does “full sun” mean?

What that means is that tomatoes need 8 hours of direct sun each day.

• Direct sun vs. full sun. All direct sun is not equal. Full sun in the afternoon in Texas will be too intense even for tomatoes, but in Oregon it’s probably OK. How close to the equator are you? How intense is your light?
  
• Sun direction. Tomatoes in the west and north will receive less intense sun than if the garden is your east and south. Take a bit of time to orient yourself before your plant.
• Season. Full sun in May is different than full sun in August. What kind of summer do you normally have? If your summer afternoons are the equivalent of a bake off, then plant tomatoes where they get 6-8 hours of morning and early afternoon sun – or morning sun and dappled afternoon sun.

2. Keep plants watered

Make sure your tomatoes are getting more than their fair share. Don’t forget – their transpiration rate is up. They’re trying to survive. When temperatures are extremely high (consistently above 90° F during the day), water plants at once, maybe two times every day. Increase frequency of watering without increasing the amount of water the plants get to avoid water logging and killing the plants.

3. Give them shade

If your garden gets too much sun, then you can provide shade for your tomato plants.

You can use many different materials to shade them. The most common to use is shade cloth  – a specialized fabric set over a structure or set on supports that drapes over plants, especially during the hottest hours of the day, 10 AM – 2 PM.

More on growing tomatoes in extreme heat and sun

Shading tomatoes: reduce their stress, keep them going in the heat ...

Heat-tolerant tomato varieties ...

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