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New Mexico State University

Issue: July 16

Hot, dry weather and soil salts can resulted in stunted tomato plants or undersized fruit

Q. I hope you can help me on this issue or can direct me to someone who can. I moved down here from Michigan so learning how to garden here is quite different. I have planted a number of crops, but have two primary issues. First my tomatoes are growing very nicely and I have quite a few tomatoes on the plants, but the tomatoes are very small. This is true for both the cherry tomatoes and the regular tomatoes. What would be the reason for this? Second, all of my vine plants ( cucumbers, muskmelon, and watermelon) are growing very nicely and have a lot of blossoms but no fruit. I see very few bees, but with the wind I would have thought that pollination would not be an issue and it is not with the tomato plants and blueberries that I had earlier. Could there be another issue?

James B.

A. Questions are changing from "What did the winter do to my plants?" to "What is the summer doing to my plants"? Soon we may be discussing the monsoon. You are not the only person who has had problems with tomatoes, chiles, cucumbers, and melons. There are many factors that may be contributing to the problems, but the most likely culprits are the high temperature, the low moisture, and soil mineral problems. In the case of the tomatoes and chiles, the primary problem seems to be a combined effect of the factors mentioned above. Low water, coupled with high heat and, often, high mineral salt content has caused stunted plants and reduced fruit size. The cold weather slowed tomato plant development and then the heat prevented proper development of the size of the fruit. Fruit size development results from water filling the cells that form the fruit. Heat and drought prevent adequate water from reaching the fruit even when the plants are well irrigated. Protection from drying winds and some shade during the heat of the day can help retain water in the plants and allow better fruit development. Salts in the soil, water, and often in the amendments added to improve the soil compound the problem. Many people having problems mention adding manure or compost to the garden. In the presence of adequate rainfall, this is good. However, when water is inadequate to leach mineral salts from the soil, plants and fruit have problems. The monsoon rains should help with all these problems. However, take care that the rains do not create a water-logged situation resulting in root diseases. The cucumbers and melons will probably soon produce fruit. These plants first produce staminate (male) flowers that only produce pollen. The female (pistillate)flowers are produced later. The high temperatures and low moisture conditions can delay the formation of the female flowers. The heat will also interfere with proper pollination of tomatoes and other vegetables, so even though they flower, the flowers will fall away due to failure of the pollen to function properly or due to the fact that the heat killed the pollen. Cooler temperatures that come with the monsoons should solve this problem. As I write this article, I see dark clouds overhead and hear thunder. The weather service forecasts rain, so you may begin to see improvements soon after you read this article. Welcome to the challenging and interesting world of gardening in New Mexico. As far as other people who can help you, you will find that your NMSU County Cooperative Extension Service has a wealth of information and people able to help with most gardening questions.

For more gardening information, visit the NMSU Extension publications World Wide Web site at

Send your gardening questions to:

Yard and Garden, Attn: Dr. Curtis Smith
NMSU Agricultural Science Center
1036 Miller Rd. SW
Los Lunas, NM 87031

Curtis W. Smith, Ph.D., is an Extension Horticulture Specialist with New Mexico State University's Cooperative Extension Service. NMSU and the U.S. Department of Agriculture cooperating.