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Plants in Mississippi thrive in the heat ‘up to a point’

I was a full-grown young adult when I first lived where cotton was grown. Cotton wasn’t part of my job at the time, but it definitely led the way for the local economy in that area, and I don’t recall if there was a second place. So I got to hear a lot of cotton talk.

One thing I heard quite a bit back then was that the hotter it gets the better cotton likes it. As with so many things, that was not exactly true. A needed addition to make the hot weather claim valid would have been “up to a point.”

Many of our food and ornamental plants in Mississippi are hot weather lovers or at least hot weather tolerant. That’s why we grow them. But with the warmest weather of the year soon to be upon us, bear in mind extremes in heat are not good for plants.

Most biological processes speed up as temperatures increase — again, up to a point.

In plants, increased energy produced by sped up photosynthesis brings about faster growth and reproduction. Whether it’s the blooms of zinnias or the fruit of tomato plants, the reproductive stages are why we plant them in the first place.

We say plants “inhale” carbon dioxide from the air for use in photosynthesis. Just as necessary is the process of transpiration, which is essentially water loss through leaves, stems and flowers.

In addition to pulling most everything up through plants as liquids, transpiration is the cooling mechanism for plants when it’s hot.

Sometimes the air temperature gets so hot a plant’s transpiration rate is no longer in sync with its photosynthesis rate. That’s when plants begin wilting and losing ground, even the heat-loving ones.

One university agronomist taught us the problem of nights too hot was worse than daytime heat. He said that’s when a cotton plant had to use too much energy running its air conditioner. Nice way to say “overworked transpiration rate,” don’t you think?

Another heat problem for plants is the sterilization of pollen. Plants differ by species as to what is the pollen-killing temperature. For example, corn pollen is not tolerant of extreme heat. Farmers around here like to plant corn in March and be done by mid-April while those in more northern states are content with May and early June planting. It’s all a matter of high-temperature risks.

By the way, every kernel of corn represents a single embryo attached to a single silk and through which a grain of pollen fallen from the tassel above moved for pollination. Corn planted abnormally late often produces ears with missing kernels because some pollen was killed by heat.

Tomato is an interesting vegetable as for heat tolerance.

During most of our summers, we see a decline in tomatoes “setting fruit” during hot spells because of pollen sterilization. But if we help the plants survive drought, stinkbugs and late blight fungi, the plants will often go back to making tomatoes right on up until frost.


Terry Rector writes for the Warren County Soil and Water Conservation District.