A Tough Year for Tomatoes

If you’re a tomato grower in Central Kansas and are disappointed with your tomato crop this year, you aren’t alone. Weather conditions this summer have made it very difficult for tomatoes to set and ripen fruit across our region.

Temperatures affect fruit set

One reason for poor fruit set is related to the timing of the heat waves this summer. Temperatures that remain above 75 degrees F at night and day temperatures above 95 degrees F with dry, hot wind will cause poor fruit set on most tomatoes. Do note though that cherry tomatoes seem to be more heat tolerant than slicing tomatoes. The high temperatures interfere with pollen viability and/or cause excessive style growth leading to a lack of pollination. Tomatoes that have already formed before the heat hits are not affected.
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Though there are “heat-set” slicing tomatoes such as Florida 91, Sun Leaper and Sun Master that will set fruit at higher temperatures, that difference is normally only 2 to 3 degrees. In general we have to wait for periods of cooler temperatures so that our tomatoes will set fruit.

Temperatures affect fruit growth

It usually takes about 3 weeks for tomato flowers to develop into fruit about the size of golf balls. Growth then becomes more rapid with the mature size being reached in an additional three to six weeks. A few more days are then needed to change color. 

The extremely hot weather we have had recently not only interferes with flower pollination but also can affect how quickly fruit grows and matures. The best temperature for tomato growth and fruit development is 85 to 90F. When temperatures exceed 100 degrees, the plant goes into survival mode and concentrates on moving water. Fruit development slows to a crawl. When temperatures moderate, even to the low to mid 90s, the fruit will ripen more quickly. 

Temperatures affect fruit color

Tomato color can also be affected by heat. When temperatures rise above 95 degrees F, red pigments don’t form properly though the orange and yellow pigments do. This results in orange fruit or different colored fruit. This doesn’t affect the edibility of the tomato, but often gardeners want that deep red color. 

Is there anything you can do to help your tomatoes ripen and have good color during extreme heat? Yes. Plan to pick tomatoes in the “breaker” stage. Breaker stage tomatoes are those that have just started to turn color. At this point, the tomato has cut itself off from the vine and nothing will be gained by keeping it on the plant.

If tomatoes are picked at this stage and brought into an air-conditioned house, they will ripen more quickly and develop a good, red color. A temperature of 75 to 85 degrees F will work well. 

Other factors

Spider mite damage

Hot summers often lead to outbreaks of spider mites and spider mites can create a ‘double whammy’ for tomato plants already under stress. Mite damage can get so severe it can kill leaves and even entire plants if not dealt with.

Consider using a hard stream of water to forcefully wash off spider mites regularly if you are noticing a problem. Be sure to carefully spray off both the top and bottom sides of the leaves to remove as many mites as possible.

Tomato diseases

Early blight and septoria leaf spot are notorious fungal disease of tomatoes in our region and can often severely damage plants when conditions are right. Check out the post below for more information on managing tomato diseases.

Don’t give up hope

It is worth the work to keep a few tomato plants in the garden as healthy as possible by managing insects and diseases. If we can keep the plants alive and growing into the fall they will continue to blossom and set fruit that can be harvested up until the first frost.