Louisiana summers are a tough time for tomatoes to set and hold fruit. The heat causes irregular flower growth in most cultivars, and the result is poor fruit set, according to LSU AgCenter horticulturist Dr. Tom Koske.
"It is true that some cultivars are now available that have genetics to beat the heat, but they still won't do miracles," Koske says, adding, "We can, however, help them to do their best with the proper culture."
Assuming you have fertile soil and are controlling pests, you can follow four treatment practices found effective in LSU AgCenter research plots. These techniques give heat-set tomatoes their best chances to develop fruit.
First, choose summer growing tomatoes that have the heat-set genetic makeup. These include Sunmaster, Solar Set, Heat Wave II, Sunchaser, Sun Leaper and Florida 91. If you have trouble finding the cultivars you want, get into the habit of starting your own from seed a month or two ahead of time. At this time of year, no greenhouse or frost protection is needed.
Second, plant deeper than usual. Normally transplants are set to just cover the root ball. For a summer crop, plant deeper to access cooler soil and better soil moisture. In fact, shallow planting may even be lethal at this time of year. Set plants in 6-inch-deep holes, up to about the first true leaf.
Third, water in the mornings. LSU AgCenter research plots were watered every other day, unless it rained, but the home garden must be watered according to soil needs. Water so that root zones are neither too soggy nor too dry. Morning watering is thought to keep roots cooler and plants less stressed than in the hot afternoon.
Fourth, mulch plants well to cool roots and even out soil moisture. Research revealed that a white or light-colored mulch was much better than the black plastic that works so well on spring tomatoes. Dark mulches get too hot in the summer.
All these treatments combined yielded significantly more summer fruit and bigger tomatoes in the research fields. For more on these topics, see our AgCenter information on tomato pests and publication 1902, Growing Tomatoes in the Home Garden.
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