Too-Hot Tomatoes and Peppers = Blossom Drop
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.
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 .