Originally Published In The Deseret News -- Wednesday, August 4, 1993
The case of the unripened tomatoes seems to be gathering a lot of interest. Never in my history as an extension horticulturist have I had so many questions about tomatoes not ripening. It certainly is not necessary to call in Sherlock Holmes for this mystery. One only needs to look at the weather patterns for the past few months and it is apparent why tomatoes are not ripening.
Tomatoes are a warm-season crop and require warm temperatures. For many years gardeners have worked to get the earliest tomatoes. While early tomatoes are great, most of us do not go through the manipulations we make for those first tomatoes to produce our later tomato crop.
This year has not been particularly conducive to good tomato fruit set. In most cases, both day and night temperatures have been too cool. Tomato plants that sit in the garden when night temperatures are below 55 degrees Fahrenheit for several hours simply sulk and refuse to set any fruit. The average low for July was only 56 degrees, so many of the nights have been cooler than 55 degrees.
Cool nights have caused the blossoms to drop on several occasions. The blossoms open, but the pollen that germinates takes so long to fertilize the plant that the blossoms drop off before they are fertilized. Gardeners who planted cool-set tomatoes that set fruits at lower temperatures or who provided additional warming by choosing planting locations or using protective devices are now enjoying the fruits of their labors. Ordinary field tomatoes, however, are painfully slow.
The solution, of course, is consistent warm weather from the time of pollination through the time of ripening. Weather is beyond the control of most gardeners. For that reason, patience and long suffering and a realization that this year's tomato crop might not be the best are the only solutions to this problem.
The next challenge is protecting the plants that we already have so that when the weather conditions are right, the tomatoes will start to ripen. Curling leaves are always a concern for tomato growers. In many cases the curling leaves are genetic. Some varieties have leaves that naturally roll and show a curled leaf. There is no cause for concern if this is the reason.
Curly top is a viral disease that causes curled leaves on tomatoes. In addition to the curled leaves, the plants are stunted and develop a yellow leaf with a prominent purple vein on the underside. Curly top is spread by the sugarbeet leafhopper, and plants were infected months ago. There is nothing you can do to correct the problem now. Plants with curly top do not continue to grow and any infected tomatoes that do ripen will have an undesirable flavor.
One of the most common causes of curled leaves is lawn weed killer containing 2,4-D. Avoid using lawn weed killers in the proximity of the tomato patch any time tomatoes are present. Distorted, curled leaves with parallel veins are the result of careless use of these chemicals. The chemical drifts and damages tomatoes that are long distances from where weed killers are applied.
Some fungal diseases have shown up in tomatoes this year because of the extra moisture. Early blight is a common problem, although not usually serious. Early blight starts out as yellow spots on the lower leaves of the plant. As the spots get older, they enlarge, develop rings and form a target spot pattern.
Early blight can be controlled by using daconil or other fungicides. Spraying is recommended only if the disease is spreading and causing serious damage to the plants. Other bacterial and fungal diseases are less common but may occasionally cause damage.
Other than protecting your plants from the problem diseases, there is little if anything you can do to improve the ripening. Fertilizers are generally not recommended after the planting. Over-fertilization of tomatoes encourages more green growth and delays ripening even further. Add fertilizer only if tomatoes show deficiencies.
Providing a few sympathetic comments and encouraging a little more patience and better luck next year are about all I can do to encourage your tomatoes and mine to ripen. Those of us waiting for an abundance of these vine ripened treats become increasingly anxious, but the reward will be worth the wait for our own home-grown tomatoes.
- LAWN WATER use this week: 1.5 inches.
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