How to help plants cope with drought and high heat rebecca latta consulting

The worst plant-damaging high heat event I’ve seen in my career happened in early July of this year, affecting plants in the San Gabriel Valley and throughout the Southern California region. Many of you have asked for help on how to manage your trees and gardens in such a severe event. I’m responding with some tips gained from my 25 years of experience promoting healthy trees and landscaping. If you have questions, please do call on me to assist you, 626-272-8444.

In the record-busting heat wave in July, mature trees dropped green leaves, buds and fruit, plants wilted, sunburned and scorched. Shoots, seedlings and potted plants wilted and died. What caused it? Climate change is promoting heat events and drought conditions here and around the world.

More extreme weather events of this nature are expected, and will continue. We need to learn strategies to protect our trees and landscaping, which I outline below.

Climate change presents significant challenges to the future of our urban landscape. As our once-mild Mediterranean climate heats up, we have to choose species that can adapt. Species such as redwood, birch, saucer magnolia, Victorian box and avocado tend to struggle in extreme heat events, and may need to be protected from heat and intense reflected light, or replaced with local natives, such as oaks and sycamores. Heat tolerant species from South America and the Sonoran desert, such as tipu, mesquite, desert willow, velvet ash, pinyon pine, California juniper, red willow, desert apricot and cypress may also be good choices.

Some plants from coastal climates can take dry soil but are not genetically adapted to high temperatures. Plants that thrive in hot conditions can feature waxy leaves, smaller leaf surface area, reflective surfaces or blue-gray color to reduce heat absorption, or can be drought deciduous, dropping leaves during dry parts of the year. Some plants store water below ground in roots or above ground in stems.

Heat damage can make plants more susceptible to opportunistic diseases and wilt, chlorosis and fruit drop. Excessive heat and sunlight can speed up disease issues. Reflected heat can do damage. Plants near hardscape, artificial turf and on sunny walls with a southern or eastern exposure can be scorched or burned. High soil temperature damages seedlings and may cause root and tissue damage that shows up later in trees and shrubs.

Provide shade. Plan ahead and plant tall annuals like sunflowers to shade smaller plants. During the heat event, use shade cloth, cardboard and patio umbrellas to protect plants from heat. Protect mature shade trees that are shading other plants in the landscape, and keep them well hydrated prior to high heat events. Wrap burlap on exposed trunks, or use a foliar spray, whitewash or latex paint on trunks for sunburn protection. Shade can also be sprayed on plants and trees in the form of a clay product called Kaolin that reflects sunlight, much as we use zinc oxide as a sun block. Apply with an inexpensive sprayer. Be sure to follow package directions and wear a mask and goggles.