The Heat is On!
How to Maintain Your Vegetable Garden When the Temperature Soars
By: Patty Cressman
Grayson County Master Gardener
It seemed like the cold nights of April would never end. But who knew the month of May would feel like July? The average low temperature for May is 61 degrees Fahrenheit, and the average high temperature is 82. Fast forward to July when the average low temperature is 73 degrees, and the average high temperature is 94 degrees. That is our current weather forecast in North Texas. With any kind of luck, June will bring back average temperatures of 69 to 90 degrees. In the meantime, keeping your vegetable garden alive can be challenging.
The optimal temperature for vegetable plants varies. Eggplant, hot peppers, okra, and sweet potatoes prefer 85 to 70 degrees but will survive temperatures ranging from 95 to 65 degrees. Blossoms may fall off pepper and eggplants if the temperature rises above 85 degrees. Corn, cowpea, and spinach prefer a range of 75 to 60 degrees but will tolerate a range of 95 to 50 degrees. Cucumbers and muskmelons prefer 75 to 65 degrees but can stand 90 to 60 degrees. Chayote, pumpkins, and squash like 75 to 65 degrees, but will survive 90 to 50 degrees. Sweet peppers and tomatoes thrive in the 75-to-70-degree range but will tolerate a daytime high of 85 and a low of 65 degrees. Tomato flowers may drop off if the temperature is above 90 during the day or above 75 at night. Chicory chives, garlic, leek, and onion, prefer a range of 75 to 55 degrees but will survive 85 to 45 degrees. Beans and lima beans prefer 70 to 60 degrees but will survive 80 to 50 degrees. Bean blossoms may drop off if the temperature remains warmer than 85 for more than a day or two. Cool-weather plants: artichoke, carrots, cauliflower, celery, Chinese cabbage, endive, Florence fennel, lettuce, mustard, parsley, potato, beet, broccoli, Brussel sprout, cabbage, chard, broad bean, collard, horseradish, kale, Kohlrabi, parsnip, radish, rutabaga, and turnip prefer a temperature range of 65 to 60 degrees but will handle a high of 75 degrees. Plants go dormant when the temperature rises above the plants’ temperature range or falls below the low-temperature range.
Extreme heat is stressful for plants. When the temperature is too high plants can suffer from sunburn and become sunscald. Plant cells experience chemical alterations and suffer from membrane damage. Plants also can suffer from dehydration. Most plant cells die at temperatures that range from 122 to 140. Often a plant will go dormant and stop growing even if they are well-watered. High heat can also prevent plants from setting any fruit because hot temperatures kill pollen.
Adequate water and shade can help reduce blossom drop and cell damage when temperatures are very warm and hot. Expect loss of blossoms or crops when temperatures deviate from the optimal temperature range for plants. Also, keep in mind high winds will increase the water demand. High humidity does help the soil retain moisture and is good for plants.
During periods of excessive heat, water the plants deeply to a minimum of six inches down at least once a week for clay and two times a week for sandy soil. Check the soil moisture using a trowel. Dig six inches deep to make sure the garden is getting enough water. Try not to let the soil dry out between watering. Do not fertilize the garden as the plants are under severe stress due to the high temperature and need to conserve energy to survive.
Keep soil covered with two to four inches of organic mulch to help keep the moisture from evaporating. Tomato, pepper, and squash plants can benefit from shade such as a shade cloth which can reduce the temperature by ten or more degrees. Keep ripe fruit well picked as ripe fruit (tomato, melon, and peppers) take necessary water from the plant. If your garden is a raised bed, remember these gardens tend to dry out quicker than a garden at ground level. Remember to keep weeds out of your garden as the weeds grow a more robust root system than vegetable plants. The stronger root system of the weeds steals necessary water from the vegetable plants.
Try not to stress too much about the weather. After all, in Texas, the seasons change from day to day and week to week. In the meantime, remember gardening is a healthy hobby that provides a person with exercise, sunshine, fresh air, and hopefully some delicious fresh homegrown vegetables.