June 23, 2009
Tomatoes Not Setting Fruit
Well, it seems as if some gardeners around the state are having trouble with their tomatoes not setting fruit. So far, that has not been an issue at my house. But my friend, Chuck Browne, the county Extension coordinator in Lee County has some thoughts on what might be the problem for these folks. Check out his guest blog below.
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Many of you have called our office saying that the flowers on your tomato plants up and fall off without setting any fruit. You are probably hoping that I have an answer for you that will stop this problem.
First, the good news is this condition is not related to any nutritional disorder or any disease or insect damage. It is related to temperature. Despite that tomatoes evolved in the tropics, flowering in tomato is sensitive to temperature. When day temperatures exceed 85 degrees F and night temperatures exceed 72 degrees F, tomato flowers will abort. An important factor involved with temperatures is this, the longer the condition lasts, the more serious the effect on flowering. Short exposures such as a week or less should not cause much of a problem. Although the combination of high day and high night temperatures causes blossom drop, high night temperatures alone can be detrimental to flowering even if day temperatures are not higher than 85 degrees F.
Now here’s the bad news. Older or heirloom, home garden varieties, which are most popular among home gardeners, are more sensitive to high temperatures than many of the newer hybrids that are presently available. When fruit do not set and all other conditions are otherwise favorable (e.g., sufficient water and fertilizer, good pest control, appropriate pH), plants generally become vigorous and dark green. Even new hybrids, however, are susceptible to blossom drop.
Commercial growers in the southeastern United States have suffered with this problem for many years until the recent advent of “heat set” tomato varieties. These varieties have been bred for tolerance to high day and night temperatures common in the summer and early fall. In fact, many of these varieties set fruit under poor growing conditions-extended cool, rainy periods as well as during extended periods of hot weather.
What to do: For this year or for an existing planting, keep the plants healthy. Keep plants watered. Maintain fertility levels and control any pest problems as any additional stress will make the condition worse. The plants will produce flowers and set fruit when temperatures become more favorable.
For next year, try growing a heat set variety. Many seed catalogs carry a wide range of tomatoes. Read the descriptions carefully looking for phrases such as heat set, hot set or heat tolerant. Often these varieties have references to their heat tolerance in their names. Varieties such as ‘Sunbeam’, 'Sunmaster’, ‘Suncrest’ and ‘Sun Leaper’ have performed well in Alabama even during during extended periods of hot weather and have become a mainstay for many of our commercial tomato growers.
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You can find more information on tomato production and blossom drop from the Alabama Cooperative Extension System here and here. This publication from Clemson University Extension has a lot of good information.