Tomatoes not ripening

I have had several inquiries lately as to why tomatoes seem to not be ripening. The tomato plant and fruit both look healthy, only not maturing. Apparently the culprit is something we really cannot control — the weather.

The fruit of the tomato plant goes through several stages of development while maturing. The tomato remains green in the early stages while it continues to grow. This can often take 40 to 50 days. When it reaches its final size, it begins to change colors. Most notably, the end opposite the stem begins to take on a white appearance. This stage is referred to as the “white star stage.” After this point, the fruit would continue to mature even if you were to pick it.

The optimum temperature range for natural ripening for tomatoes is 68 to 77F. If the average temperature strays from this ideal range, the ripening process will take longer. If temperatures are above 85F for extended times, then the tomato plant will not produce lycopene and carotene which are the pigments responsible for the ripe color in tomatoes. 

Are some of your tomatoes plants experiencing this problem, but others are maturing normally? The most likely culprit is that certain varieties of tomatoes are more sensitive to this hot weather than others. When the temperatures cool back down, the ripening process should go on normally.

Tomato tops not maturing

There also is a condition in which the top of the tomato fruit does not ripen, but the rest of the tomato does so normally. This condition is called “yellow shoulders,” and is linked to high temperatures as well.

The chlorophyll in the top portion of the tomato does not break down properly in the maturation process, leaving the tissue corky and discolored.

One way to avoid this problem is to make sure the tomato fruit are not receiving too much sunlight, but instead covered with leaves. Direct sunlight on the fruit has been shown to increase the likelihood of yellow shoulders. A tomato suffering from yellow shoulder is safe to eat, just cut out the discolored parts.

Educational programs of the Cooperative Extension Service serve all people regardless of race, color, age, sex, religion, disability or national origin. 

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