Summer heat takes its toll on gardeners and their plants. You and I get relief by seeking shade, air conditioning or cool lemonade. Unfortunately, plants are at the mercy of Mother Nature and the gardeners who care for them.
Plants suffer several maladies from heat and the attendant problems. Plants have temperatures at which they grow best, temperatures that they tolerate and temperatures that are lethal. Ambient air temperatures are not the only consideration. Leaf temperatures are also important. Radiant heat raises temperatures well above the air reading. Plants have their own cooling systems. The most vital is the transpiration system where the plants move water through their vascular or circulatory system and cool their leaves by evaporative cooling. The needs and efficiency of this system depend on relative humidity, wind speed, solar radiation and temperature.Protection from heat problems starts with adequate water. Unfortunately, this idea is not well-understood even by experienced gardeners. The natural tendency is to water, water and water when the temperatures rise. However, overwatering kills more plants than underwatering. Learn to judge your soil to provide the most efficient water use. Plants in light sandy soil need water more frequently while those in heavy clay can go longer between watering.
Another way of looking at the water-holding capacity is that 1 inch of water applied to sandy soil may penetrate 18 inches. The same amount applied to clay may only soak the soil 6 inches because it has a greater water-holding capacity.
Excess water in clay soil does not drain away but remains and excludes the oxygen from the roots. Without oxygen the roots die. Water molds also grow in moist environments and further damage the roots. The result is when water does not get to the leaves the leaves will scorch or burn. Symptoms of overwatering are the same as drought, so many times the wrong cure is applied, making the problems worse.
Plants can still show damage from the heat even if there is sufficient water in the soil. Trees with large leaves are most sensitive as they cannot move water fast enough to prevent burning. Maple, horse chestnut, walnut, poplar, aspen and linden are susceptible. The most common symptom is browning of the edges of the leaves and between the veins of the leaves. Leaf scorch is usually not fatal, but the symptoms remain until the leaves drop.
Heat stress on turfgrass readily shows as brown spots in the lawn. The best way to prevent the problem is to water the grass according to its needs. The total water needs of the turf is around 1.5 inches per week during the hot weather. Remember that the amount of water needed by the turf does not vary. Turf grown on sand uses no more water than that grown on clay. What differs is the water-holding capacity of the soil. Since sand holds less water, an application of a half-inch of water three times per week should keep the grass green. Turf on clay soil may stay green with a single application of 1.5 inches of water per week.
To measure the amount of water applied, place several large straight-sided gallon cans randomly across the lawn. Run the sprinkler for 30 minutes and then measure how much water collects in each can. Average the amount in each can to determine how much water is applied in a given time.
Check the sprinkler system for proper coverage. The most common cause of brown spots in the lawn is a system that does not operate correctly. The most common response for a brown spot is to run the system longer. It makes no sense to overwater most of the turf and waste water for one dry spot. Fix the sprinkler equipment to solve the problem.
Heat also affects vegetables. Tomatoes and beans do not pollinate and drop their blossoms if temperatures are above 90 degrees Fahrenheit. Tomatoes, peppers, eggplants, melons and squash also develop brown leathery spots on the blossom end when temperatures rise. Blossom-end rot is caused by an internal calcium deficiency in the fruit triggered by hot dry weather. When it gets too hot, cool-season crops stop growing. They then develop strong flavors and coarse textures.
Heat also dooms the cool-season flowers. If you have not yet learned that the time to plant these is in the fall, the summer heat will teach you. During the summer these flowers struggle and fade and usually succumb to mildew or root rot.
Heat, drought and the accompanying environmental problems need not mean the end of gardening. Properly managed, they are minor setbacks. The desert we live in is often unforgiving to plants as they cannot protect themselves. Take refuge from the heat yourself and protect your plants by watering them as needed. Protect them from other stresses and they will survive to beautify and produce in your garden.
- THE UTAH HEMEROCALLIS (DAYLILY) SOCIETY invites the public to tour the Salt Lake City gardens of society members. The following gardens will offer a chance to view peak daylily bloom within a garden setting:
Saturday, July 13, 8 a.m.-2 p.m. - Brad Swedlund, 381 H St.; Tom and Teresa Browning Hess, 1797 Park St.; Richard and Elaine Randolph, 7120 S. Nutree; Gary and Joann Rieben, 9861 S. Solomon Circle; and Craig and Sue Pyper, 3514 Country Hollow Drive.
Sunday, July 14, 8 a.m.-2 p.m. - Don and Beverly Sudbury, 1258 Lavon Circle, and John and Mary Jim English, 2453 E. 3080 South.
The Hemerocallis Society show and sale will be Saturday, July 27, at the Sugar House Garden Center.