Tomato Harvest Down? Blame the Heat

A recent string of comments on the University of Minnesota Extension Master Gardener listserv answered a question I’ve been wondering about: Why  do my tomato plants look so stellar and yet have very few fruits? The short answer is blame the heat.

Blossom drop is a fairly common problem with tomatoes (though not the problem I usually have). What happens is that your plants look great, with lots of green foliage, put out plenty of blossoms, and then the blossoms just wither up and drop off the plant. I noticed this happening almost a month ago, and my first concern was that bee numbers might be down (unfounded, it turns out) and perhaps the fruits were not getting pollinated.

But the Master Gardeners pointed out that the combination of high temperatures and high humidity—exactly the weather pattern we have been stuck in for several weeks—is a frequent cause of blossom drop. Tomatoes like daytime temperatures between 70 and 85 degrees F and they don’t like the humidity to be above 70 percent. We’ve been in the 90s frequently and above 70 percent humidity regularly.

Moreover, the amount of rain we’ve had and its tendency to come in deluges could be washing away some of the nitrogen the plants need, also contributing to blossom drop. I’m growing a few tomatoes in pots and a few in the ground, and the ones in pots got a good shot of worm-poop fertilizer a couple of weeks ago, so I do not think that is my main problem.

I’m hoping the weather may correct itself soon and the plants will get a chance to set more fruit. In the meantime, I’m coddling the few tomatoes that are ripening on the vine.

2 Replies to “Tomato Harvest Down? Blame the Heat”

  1. Aha, so that is what has been happening to my tomatoes this year. Last year they were planted in a low-lying area and flooded, so this year I moved them to higher ground and they look fantastic…….but very few fruit. Good to know the reason why, oh, well, there’s always next year.

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