Advice During the Heat of Summer

Q. Can you give some tips to on how to survive this latest bout of heat? Is it simply too hot right now for plants? Is shade cloth the answer?

A. It has been hot these past few weeks and very stressful for many landscape plants. There has been a combination of high temperatures, intense sunlight, very low humidity and windy conditions. Just like us, healthy plants have the best tolerance to the extremes of heat and cold. But water and fertilizer can be a killer if too much is applied.

            Shade cloth is helpful in some situations but it is usually for vegetables. Use shade cloth to manage the intensity of sunlight and reduce sunburn on tender vegetables. Shade cloth providing somewhere between 30 to 50% shade is used with these plants. Otherwise, rely on leaves of plants to provide their own filtered light.

Avoid watering trees, shrubs or any plants that are woody every day. Try to give these plants at least one day of rest, without irrigation, between waterings. Some landscape plants have roots that suffocate easily if the soil contains too much water. These plants seem to “die overnight” when watered daily or the soil remains wet.

Mulch helps. Mulch of any kind, whether it is rock or wood chips, applied to the surface of the soil helps cool it, preserves soil moisture and helps battle weeds. Rock mulch applied to the surface of the soil is best for desert species of plants. Woodchip mulch is best for non-desert species of plants. A surface layer of mulch can add one or two extra days between irrigations.

A wet sponge drips water because it can hold no more.
A sponge is moist after it has been squeezed.

Water just before the heat. Make sure plants enter the heat of the day with their roots surrounded by moist soil. There is a difference between “wet” and “moist”. This is particularly true of plants grown in containers. These soils dry out faster than soils in the landscape. Plus containers warm their soils faster compared to landscape soils. Wet or moist soils warm up slower than drier soils.

             

Water lawns early in the morning. Apply lawn irrigations as close to sunup as possible but when still dark. Windspeed is usually slowest at these times. Never put a lawn “to bed” wet. Give the leaves a chance to dry off before it gets dark. This helps avoid lawn diseases.

            

Fertilizer can be applied now. You can apply fertilizers this time year but use half the recommended rate and apply it when temperatures are cool, during the mornings or evenings. Make sure dry fertilizers are rinsed into the soil immediately after they are applied. Lifertilizers can be sprayed on leaves but only during morning when temperatures are cool.

             
Some pruning can be done now. Light pruning can be done anytime during the growing season. Never use anything bigger than a hand pruner this time of year. Use saws and loppers only during late fall winter and early spring. Don’t remove too much. Always leave some growth to shade the trunk, stems and branches.