Too-Hot Tomatoes and Peppers = Blossom Drop

flower of brandyine tomato

Will these Brandywine blossoms make it to tomatohood if the weather stays hot hot hot?

Our friend Melinda writes:

“It’s been my understanding that when it’s too hot for a sustained period (including high overnight temps–like around 80), that many veggie plants drop their flowers before they fruit (e.g., tomatoes, peppers, squash, etc.). Is that true in your experience?”

Yes, but less often than you might think – or fear, given the ongoing heat wave. High night temperatures sterilize pollen and flowers that are not pollinated fall from the plant. But the window for this kind of blossom drop is comparatively narrow.

Pollen forms before the flower opens, but not that long before, and after the flower opens it must  be pollinated within a day or two (over the course of a single morning, in the case of squash), no matter what else is going on.

cherry tomato blossoms and fruit

Maglia Rosa cherry tomatoes on the way

After the flower has been successfully pollinated the baby fruit won’t be affected. Or at least it won’t be affected by high temperatures. The drought that may accompany the heat and the fungus diseases encouraged by high humidity are another story.

Meanwhile, back at the thermometer, the thing to keep in mind is that flowers are forming more or less continually and maturing ditto, so even if one or two or three fall, more should soon appear to take their place.

Example: The Maglia Rosa cherry tomato in the picture is growing in the greenhouse, where I do not keep a thermometer because there’s nothing I can do if it gets too hot. Nevertheless, I know it must have been well over 100 in there for at least two days after the formation of the fruit on the left.

Nothing has dropped yet, and maybe nothing will ( see below) but even if the branch isn’t filled there will be tomatoes on it.

Tomatoes start suffering when nights are warmer than 75 degrees; flowers fall at around 80. Peppers – it figures – are cool up to 80 but drop if it goes over 86. Days over 95 spell trouble for everybody.

Fortunately, still being 80 when dark descends and staying at 80 all night are very different things. Individual varieties have different heat tolerances. Shade matters, during the day, for plants as well as people. Good leaf cover can save flowers that would die in direct sun.

The numbers make it sound as though you could look at the thermometer and know how hungry you’re going to be, but it’s more of a crapshoot than that, so don’t get discouraged.

Do try to be sure that what pollen there is gets transferred. Tomatoes and peppers are both self-fertile, but the pollen must still move from the male to female parts. If insects are in short supply and the air is still, gently brush/stroke/shake the flowers or use a fan to provide a light breeze.

You can also play cupid with a cotton swab, if you don’t have many plants or much else to do with yourself.

All that said, successful pollination will only get you so far. Tomatoes and peppers will rid themselves of new flowers and new fruit when deeply stressed, no matter what the cause. They’re conserving their energy so at least a little fruit will ripen and produce viable seeds. If the situation is really grim, consider removing some flowers yourself. After the weather moderates (it’s got to, or we’re all toast), plants that haven’t been struggling in vain will be stronger and better able to take up where they left off .

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  • Gosh, I can’t thank you enough for all this! Last year I did the plant husbandry thing (using a small paintbrush) with my Delicata squash. Also tried saving male flowers in fridge till females opened. Ended up w/ ~4 squash from each plant, which wasn’t too bad, considering how cold & wet it was last summer. But I haven’t tried the fertilization tricks yet this year w/ tomatoes & peppers. We’ll see how it goes–the brush is always there! Thanks again for all of this! You have some tomato varieties I’ve not heard of (though that’s not surprising, given the extent of your gardening activities and knowledge)–e.g., Maglia Rosa. Is it an heirloom?

  • Naseer Said,

    Thank you for the thorough post on this topic. I’ve certainly read before that tomato plants dislike too-hot nighttime temps, but I didn’t understand fully why or to what extent the damage can occur.

  • Rachel Said,

    I’m starting to wonder if I’m going to get any fruit from my tomato plants. I have yet to see one single measly tomato, and haven’t even seen that many blossoms. I may have to throw in the towel with the ‘maters, since I’ve never really been successful growing them, and just get tomatoes from the farmers’ market. *sigh*

  • Bonnie Said,

    My tomatoes are doing fine, actually I had some of the first tomatoes around. Now my cucumbers – that’s a different story. The few I’ve picked are curled up little things or round balls. I’ve read lack of pollination could cause this. No matter, the plants are drying up anyways. I guess it’s off to the Farmer’s Market to buy my cukes.

  • Steve Said,

    I’ve harvested about 65 lbs. of ‘maters so far (17 plants planted on 4/28), but the blossom drop has gotten really bad here (Indiana) after the extreme heat arrived. For awhile I was shaking the plants at night, & it seemed to help a lot, but I got out of the habit when the mosquitoes got bad! I had read that tomatoes pollinate better at night, y’all might try it if you can stand the bugs.

    Welcome, Steve, and congratulations on the harvest! – or at least the start of same.

    I’ve never read that tomatoes pollinate better at night. Guess that might be true of the self-pollination if night humidity made the pollen heavier or something, but my guess is that your good work was what did the trick, spreading the viable pollen as widely as possible, and that you’d have the same success whenever you were able to go out there and shake ’em. For what it’s worth, tomatoes’ primary natural pollinators are bumblebees.

    I don’t know how long your growing season is naturally, but if it’s anything like ours those first tomatoes are/were early and you have all kinds of time for new crops to form and ripen before frost.

    May it be so!

  • Tom Said,

    Thanks everyone and especially for the article. I am in Oklahoma and we lost all the maters in 2010 pretty much. The heat is back to high 90s day/low 70s night in the first week of June 2011 (again), and I am afraid of losing my beefboys and rutgers which are just now pollinating. One old tale is that pioneers and grandmas put burlap material over the tomatoes to protect them from direct sun and they grew. I noticed the only two formed tomatoes so far are deeply shaded by renegade corn plants, and last year I had tomatoes during over 100 weather buried deep inside big bushes. I stretched black ground cloth over the trellises to simulate shade and the yellow blossoms have reappeared in plenty. Has anyone had experience with this?

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