The hottest weeks of the year are just ahead for us. We see the highest daytime temperatures of the year in July with short hot nights and longer hot spells. These are some of the worst growing conditions possible.
Here are a few key pointers to minimizing heat stress and keeping plants alive in July.
▪ Fertilizing: When daytime temperatures are consistently above 95 degrees, plants’ roots continue to draw up water but the stressed plants stop growing and stop producing new flower buds and leaves. Roses set few if any buds and the buds that bloom in July have paper thin petals with little or no fragrance. Tomato and bean flowers drop and no new flowers appear until late summer when daytime temperatures cool and nights are longer and cooler.
Fertilizing heat-stressed plants to encourage new growth further stresses the semi-dormant plants. Stop fertilizing or cut way back on fertilizer amounts and times until mid-August. If you do fertilize, avoid applying high nitrogen fertilizers (especially liquid formulations) and instead apply low number granular fertilizers that slowly release nutrients over a longer period of time.
Fescue lawns normally go dormant during the summer months and require less water and no fertilizer. Bermuda lawns thrive in the heat, but they do well without a July feeding. Set mower blades high so that longer grass blades shade the roots.
▪ Irrigation: Be prepared to adjust irrigation timers frequently in July to conserve water on cooler days and to keep plants from wilting or dying during the hottest spells. Monitor irrigation systems for problems frequently as well.
Deep irrigate fruit and nut trees especially citrus when the top 3 to 4 inches of soil is dry. That may be every four to five days in July. The primary cause of crop loss is insufficient watering during the summer. Use bubblers on a hose or soaker hoses to allow water to slowly percolate to a depth of at least one foot. Most of a tree’s roots lie within the top foot of soil. Place irrigation devices directly under the drip line or outer edge of the canopy where the feeder roots take up the most water.
Warm season grasses including bermuda need about 85 minutes of watering July. Cool season grasses (fescues, Kentucky bluegrass, perennial rye) require 113 minutes of irrigation, depending on irrigation sources and types. If the grasses turn blue-ish and you can see your footprints easily, the lawn is too dry.
▪ Pesticides and herbicides: High temperatures vaporize many pesticides and herbicides as they are sprayed. Foliage can be injured by pesticide sprays when temperatures are over 95 degrees.
Read product labels carefully for temperature guidelines and do not spray any chemicals when bees are foraging and flying. Pest insects proliferate during hot spells when plants are stressed but so do beneficial insects that prey on pests. Wash dust off plants often; dust clogs plants’ breathing pores. Red spider mites build their webs on the undersides of dusty plants; they can be washed off with a blast of water from the hose.
Send Elinor Teague plant questions at firstname.lastname@example.org or email@example.com (“plants” in the subject line).