The Literary Gardener – July 2016

“Heat, ma’am! It was so dreadful here that I found there was nothing left for it but to take off my flesh and sit in my bones.”
~ Wit and Wisdom of the Rev. Sydney Smith, 1856

Reverend Sydney Smith (1771-1845) was an English humorist and writer who became a clergyman because his family didn’t approve of his first occupational choice, which was to practice law. Too bad, a comedic attorney would have been refreshing. No matter, Smith’s off-the-cuff witticisms so delighted his parishioners that his sermons drew standing-room-only crowds.

With his complaints about the heat, I wonder if Rev. Smith would have found humor in World Naked Gardening Day? Inaugurated in 2005, gardening in the buff is celebrated internationally on the first Saturday of May. Be sure to mark your calendars for 2017 if you missed it this year.

Gardening naked is certainly a way to beat the heat of July, but think of the sunburns! Better yet, gardeners can work during relatively cool mornings and evenings. What about our plants, though? How do they cope with summer’s high temperatures, and how can we help our plants stay healthy when it’s hot?

Most garden plants tolerate summer temperatures up to 90-degrees F. Plants become stressed when temperatures rise higher—the longer the hot spell, the more stressed they become. Like people, the weakened state makes plants more vulnerable to disease; insects are also more likely to attack weakened plants.

In addition, excessive heat shuts down crucial plant processes. One is transpiration, a major mechanism for plants to dispel internal heat by releasing water vapor through their leaves. People perspire, dogs pant, plants transpire. Extreme temperatures trigger leaf pores, called stomata, to close, which interrupts transpiration and causes internal leaf temperatures to rise still more. In essence, plants become feverish. Plant temperatures around 115-degrees F. result in tissue die-off. At the same time, stomata closure prevents the plant from photosynthesizing.

Heat damage to plants is most prevalent on hot, windy days when moisture evaporates from leaves faster than the plant can absorb water from the soil through its roots. Of course, soil dries out more quickly in hot weather, and this makes the problem even worse. Shallow-rooted and container plants are particularly susceptible to heat injury, whereas drought-tolerant plants have developed adaptations to absorb water quickly, lose water slowly, or both.

Plants show the first sign of heat stress by wilting. Sun-scorched leaves turn dry and brown at the tips or edges first. Sunburned leaves, stems and fruit develop bleached-out areas. Many vegetables, including tomatoes, peppers, and squash, won’t set fruit when temperatures reach past 90-degrees F. Their flowers and immature fruit will drop off as the plant switches into survival mode.

Key to keeping garden plants healthy during hot weather in July is providing enough moisture to the soil—perhaps even twice as much as is normally needed (which is about 1 inch of water a week or 65 gallons per 100 square feet.) Although daily watering may be necessary, it’s most important to water deeply so moisture reaches the plant’s root zone about 6 inches down. Keep in mind that some fruits and vegetables will behave badly by splitting if the soil is thoroughly saturated after it has become very dry. Drip irrigation is usually the best method for providing consistently even and deep moisture to garden plants.

The best location for raised beds is oftentimes the eastern side of property where the plants enjoy some afternoon shade. Otherwise, during hot spells it will be necessary to provide shade by setting up screens or umbrellas, or by using 30-40 percent shade cloth or a lightweight floating row cover. Using these measures of heat protection can reduce plant temperatures by 20 degrees, but be sure to secure shade covers against wind and position them high enough to allow airflow around the plants.

Mulching around the root zone of garden plants is another way to retain moisture, plus mulch cuts down on weeds that compete for water and nutrients. The downside of mulch is that it, too, absorbs water; also, the bane of my summer gardening life—the voraciously hungry earwig—considers mulch a five-star hotel.

In 2015, Jackson County residents confronted 19 days in July when temperatures rose above 90 degrees; chances are good that we’ll have just as many, if not more, hot days this summer. So, gardeners, let’s put on our hat, sunscreen, and insect repellent, and bring a bottle of water for ourselves, and go cool-off our thirsty garden plants. As the Rev. Sydney Smith preached,

“It is the greatest of all mistakes to do nothing because you can only do little—do what you can.”