The recent heat wave hit plants in my yard pretty hard. The wildflower butterfly meadow, on a slope out by the main road, looked super all spring and up through the first half of June when warmer-than-normal spring temperatures paired with two or more rain showers each week. The end of June was an entirely different story. That’s when my community had a string of days where the mercury topped out between 90 and 103 degrees Fahrenheit every afternoon. I know some of our readers who live at lower elevations than we do had record setting temperatures higher than that. We got heat lightening and thunder, but no precipitation. My wildflower and daylily blooms dried up. The lawn along with most flower stems and stalks in my gardens look bad. (“Crispy” is the way my friend Susan describes her sun-baked plantings.)
Woodland understory plants and trees on our property suffered too, despite the cooling effect of shade in the woods. Thanks to early morning irrigation, up by the house newly planted flower containers and one flower bed (along with the nearby lawn that got overspray from the sprinkler for that flower and herb garden), my strawberry plants and the vegetable plot survived this hot, arid spell.
In times like these, gardeners need to irrigate wisely. Poor watering practices can weaken plants making them susceptible to diseases. Weak plants or those in poor health have difficulty fending off insect pests. Most garden and landscape plants need at least one inch of water (from rainfall and irrigation combined) in every seven-day time period. Some varieties of turf grass, young trees and shrubs installed within the last two or three years, other moisture-loving plants and plants growing in containers, need more than one inch of water each week. Irrigate infrequently. Do not water every day and certainly not more than once per day. Applying water too often and just enough in each instance to wet the top of the ground, encourages shallow roots. Should a homeowner be unable to irrigate because of high water costs or because their community restricts water usage during periods of drought, shallow-rooted plants will be the first to suffer. When you do irrigate, apply enough water to moisten soil a few inches below the surface. Water plants in pots or other containers to the point of runoff through drainage holes. Irrigate early in the day so moisture on stems and leaves dries before late afternoon. Wet foliage at dusk and overnight makes conditions right for development of fungal diseases.
Just as plants reproduce from seeds, fungi develop from spores. Because spores are microscopic and light weight, they are easily airborne. Most spores remain vital despite freezing temperatures. Once dispersed by winds and/or splashing water, spores remain on plant surfaces or in soil a long time. If temperatures and moisture conditions are right, spores in contact with susceptible plant tissues generate fungal diseases. Damp/wet leaves at night provide an environment that favors fungal disease infections. If soil becomes severely parched, the tiny root hairs that do most of the work bringing moisture and soil nutrients into plants can die. After such damage occurs, the plant can’t get the water and nutrients it must have. Sitting in soggy soil causes similar problems. Landscape plants with roots impaired by either too much or too little water, are prone to root rot fungi. Root rot threatens the infected plant’s survival. Another problem caused by uneven soil moisture (at times too dry and other times water-logged) is blossom end rot in tomatoes. Damaged tomato roots don’t absorb enough calcium. Without sufficient calcium the plant does not form healthy tomatoes.
Plateau Gardening is written by Master Gardeners for gardeners in Tennessee’s Upper Cumberland Region. UT Extension Cumberland County at P.O. Box 483, Crossville, TN 38557 (931-484-6743) has answers horticulture questions, free publications and details on how to become a Master Gardener. Send email comments or yard & garden inquiries to Master Gardener Rae, firstname.lastname@example.org.