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Hot Weather Garden Woes

Hot Weather Garden Woes

By Melinda Myers for Milorganite
Photographs by Melinda Myers, LLC

No fruit on your sweet peppers, misshapen tomatoes, and squash not flowering? Blame it on the weather. Temperature extremes can interfere with flowering and fruit set on these and other vegetables in your garden.

It is certainly frustrating to watch and wait for that first red, ripe tomato. These vegetables thrive in warm, sunny conditions, but temperature extremes can prevent fruiting, cause misshapen fruit or reduce the size of the harvest.

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When daytime temperatures rise above 90°F and night temperatures remain above 70°F, blossom drop and poor fruit development may occur. Combine this with low humidity and the pollen is not viable. In hot and humid conditions the pollen is too sticky and doesn’t move from the male to the female part of the flower. Without pollination the flowers won’t be fertilized and fruit will not develop.

Cool weather can result in poor fruiting. Night temperatures below the optimum of 59° to 68°F will reduce the amount and viability of pollen that the plant produces. Less viable pollen means fewer fruit will form. Cooler temperatures below 55°F can result in misshapen fruit and catfacing (photo below). The malformed fruit is still tasty and safe to eat.

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Temperature extremes also impact pepper productivity. When temperatures climb to 95°F or higher the pollen is sterile and flowers may drop. Small fruit may also fall from the plant during such hot spells. Pepper plants also experience poor fruit set when night temperatures drop below 60°F or rise above 75°F.

Tomatoes and peppers aren’t the only vegetables impacted by temperature extremes. Eggplants, a close relative to tomatoes and peppers, do not set fruit until night temperatures are above 55°F. Beans stop flowering or the flowers die when temperatures rise above 85°F.

Flowering in squash and cucumber plants is also influenced by temperature and other environmental factors. These plants produce separate male and female flowers. The male flowers usually appear first and it is not until both the male and female flowers are present that pollination, fertilization, and fruit production can occur.

Research found cool temperatures, bright sunlight, and shorter days encourage female flower production while male flowers are more prolific during warmer temperatures, less sunlight, and close spacing. Flowering on squash and cucumbers is also impacted by nitrogen fertilization. Too much can prevent female flower formation while insufficient amounts can reduce the number of male flowers. Using a low nitrogen, slow release fertilizer, like Milorganite, can provide small amounts of needed nitrogen over an eight week period.

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We can’t change the weather but understanding its impact eliminates the mystery as we wait for our gardens to produce. The simplest solution is to wait for optimum temperatures and the proper humidity levels to return. Once this happens the plants will begin producing fruit.

When hot weather does arrive be sure the plants receive ample moisture. Mulch the soil with shredded leaves, pine straw or other organic matter to keep roots cool and moist. Provide a bit of cool afternoon shade and shelter from wind to further reduce heat stress.

If poor productivity due to temperature extremes is a yearly issue, consider planting more heat-tolerant varieties, adjust planting times and look for more suitable growing locations.

When the harvest is delayed, consider extending the season with the help of row covers. Loosely cover plantings with the fabric and anchor the edges in place with stones, boards or landscape staples. These spun fabrics allow sunlight, air, and water through while trapping heat around the plants. Cover plants when frost is in the forecast and leave in place. Just lift to harvest and secure the fabric when done. Remove the row cover when you decide the season is over.

As a gardener, you know that in some years your garden is more productive than in others. And fortunately there is always next year.


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