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Science-based gardening information for Colorado communities from CSU Extension, Denver Botanic Gardens, and Green Industries of Colorado.

1835 – Tomato Questions Abound in Heat   arrow

Why are the blossoms falling off my tomatoes?

This is one of the most common questions in July. High temperatures particularly when coupled with drying winds interfere with pollination. Un-pollinated flowers dry and won’t remain on the plant. Tomato pollen is transferred within the same flower by shaking of the plant and is not wind or insect carried. Windbreaks, insuring consistent moderate moisture in the soil, and clustering plants may be somewhat helpful in preventing blossom drop.

Why aren’t my tomatoes growing very fast?

Other tomato complaints have centered on why plants haven’t grown as fast as usual or why fruit is not sizing or ripening. The answers are again environmental. Front Range tomatoes often get a late start due to cold night temperatures that can last into the second week of June. Three nights that week with temperatures below 40 degrees F can set back newly planted plants. These plants can take several weeks to recover and resume active growth.

What temperature is best for tomatoes?

Tomatoes have the reputation as being heat lovers probably because they are intolerant of spring cold. They only tolerate so much heat and fruit does not increase in size at temperatures over 95 degrees F. July and early August can bring many days above 90 degrees F.

Tomatoes grow best at uniformly moderate temperatures between 65 to 85 degrees F. This is why a high altitude, semiarid climate like Colorado with wide daily temperature swings is not a favorable area for tomato growing. Days are often too hot and nights are often too cold during the growing season for tomato growth and fruit development.

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