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University of California Cooperative Extension Ventura County
669 County Square Drive, Suite 100
Ventura, CA 93003
Phone: 805.645.1451
Fax: 805.645.1474
Office Hours:
Monday - Friday from 9 a.m. to 4 p.m.
The office will be closed for the following holidays:
November 28-29 - Thanksgiving Holiday
December 24-25 - Christmas Holiday
December 31 - January 1 - New Year Holiday
Tomato Fruit Set
Tomatoes are a “warm season” crop. They are native to central and South America. As such they are sensitive to cool temperatures. Tomato flowers are self-fertile, i.e., the pollen (male) of a flower can fertilize the egg (female) of the same flower. However, if night time temperatures are cold (60º F or less at night), the egg is not receptive to pollen and fertilization does not occur. Unfertilized flowers abort. This is a common problem on the Central Coast. Temperatures are not cold enough to prevent growth, but are too cold to permit flower set. Hence, we have nice, healthy plants with no fruit.
Tomato varieties vary in their flowers’ sensitivity to cold. Some tend to start setting fruit earlier than others. Many of the heirloom varieties have no tolerance to cold at all and will probably not set fruit until early to mid-summer, i.e., late June to early July.
While I am on this subject, I will add that often the first flowers that do set produce fruit that is wrinkled and deformed. If you slice these tomatoes in half between the stem and blossom end, you will note that several of the seed locules (jelly-like areas where the seeds are) are empty (no seeds). This is due to incomplete fertilization. Every potential seed in a tomato must be fertilized by a pollen grain. If this does not happen, the fruit may be partially pollinated. That is, enough to set the fruit, but not enough to set all the seeds. The seed locules that are not fertilized do not develop normally, thus the deformed fruit.