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The Homeowners Column
Heat brings problems for vegetables
State Master Gardener Coordinator
Bad tempers and bad hair. High electrical bills and low motivational ills. Just a few of our symptoms from too much time spent in too much heat. Our garden vegetables also suffer from outrageous heat.
Vegetables and vegetable lovers tolerate more heat when they are well-hydrated. Unfortunately some vegetables yield poorly during high heat even when the plants get plenty of water. Fortunately most of these problems subside once temperatures moderate.
Vegetables vary in their tolerance to summer's heat and drought. Sweet potatoes are heat lovers. Sweet corn plants may look fine during hot dry weather; however, corn kernels fail to form at the tips of ears if dry weather occurs during silking and pollination. Leafy crops such as lettuce and spinach flower quickly and may taste bitter under high temperatures. Broccoli may produce loose heads and quickly flower during long summer days. As their name implies cool season vegetables including cabbage, cauliflower, Brussels sprouts and kohlrabi prefer cooler weather and produce a better crop when planted early in spring or planted later in summer so they can develop during the cool weather of autumn.
Sometimes the plants do fine in the heat, but the vegetables temporarily fail to form fruit. The flowers of tomatoes, peppers and green beans may drop and fail to form fruit during periods of extreme heat especially when heat is combined with hot dry winds or warm nights (above 70°F). Heat may also affect fruit development in some pumpkin varieties. Extended periods of night temperatures above 80 °F tend to favor development of more male flowers rather than the female flowers needed for pumpkin development.
Tomatoes and peppers can also experience sun burn. Typically fruits are borne safely tucked in toward the interior of the plants where leaves protect them from the full blast of sun. However when tomato or pepper leaves are lost due to the munching of tomato hornworms or loss due to leaf spot diseases, the fruits are exposed to too much sun. In immature fruits the sunburned areas appear light green and feel soft and mushy. As the fruit matures the affected areas become tan to white, papery dry and sunken. If possible, plants with a receding leaf line should be shaded with sheets, floating row covers or shade cloth.
Drought conditions coupled with high humidity can also cause small, sunken black areas near the end of tomatoes and peppers. This condition known as blossom-end rot is caused by a calcium deficiency brought on by drought, uneven water availability or from root damage due to deep hoeing or tilling. Peppers and tomatoes with blossom end rot and sun burn are still edible, but should not be used in canning and freezing.
In some tomato varieties fruit cracking or splitting can also occur particularly when an extended dry period is punctuated with a heavy rain or irrigation. Next year consider planting crack resistant varieties such as Celebrity, Big Beef, Jetstar, Juliet, Rutgers and Sweet 100.
So what can we do with our solar heated gardens? Regular watering can help alleviate some problems. Remember to water the soil and not the leaves. Try to keep soil consistently moist by watering with soaker hoses or slow watering with a hose directly to plant bases. Ideally soil should be moist to eight inches deep. This may require one inch of water every couple of days depending on the weather and garden soil type. Avoid sprinklers since much of the water is lost through evaporation. Mulch with three to four inches of organic mulch such as compost to help maintain soil moisture and moderate soil temperatures. Avoid deep cultivation.
A bit of good news if you like heat pumped peppers. Long hot dry summers produce the best and hottest chili peppers.