Serving Larchmont Village, Hancock Park, and the Greater Wilshire neighborhoods of Los Angeles since 2011.

Caring For Trees in Extreme Heat

Trees planted last year in Hancock Park by the Hancock Park Homeowners Association under the direction of arborist Sabine Hoppner. (photo from Hancock Park HOA)

Tress are a vital part of our urban ecosystem. They clean the air, provide habitat and shade for humans and animals living in our cities. Like humans, trees struggle in extreme heat. We asked the Hancock Park Homeowners Association’s arborist Sabine Hoppner for advice on what we can doing to help our trees get through this current heat wave. Temperatures are expected to climb into the 90s early next week. 

The current heatwave is particularly difficult to endure since it is lingering longer and is hotter than in the past, and we just came out of an unusually cool and wet spring. This is true for trees, too. Heat stress symptoms in trees usually show up when the temperatures are above 90 degrees F and increase with rising temps.

Here are some tell-tale signs to look for:

  • Leaf drop
  • Blossom and fruit drop
  • Little or no new growth
  • Scorched leaf margins
  • Leaf rolling
  • Wilting during the cooler night hours

These are all signs that the tree cannot take up enough water to support the entire canopy. Trees can regulate their water budget by closing the stomata (microscopic pores in the leaves), which in turn leads to reduced photosynthesis and growth. The tree shuts down to wait out the lack of water and the heat. This is fine for a few days, but becomes damaging if it goes on for too long and the tree is forced to use more drastic measures such as leaf drop and wilting.

Ideally we keep our trees well hydrated and therefore resistant to heat stress, however, a brutal heatwave following a cool spring might catch us off guard. If you notice the above listed stress symptoms on your trees please do the following:

  • Water deeply and infrequently; a deep weekly soak is much more efficient than daily shallow watering.
  • Pay special attention to younger and newly planted trees, as they do not have the root systems in place yet to support themselves; watering bags such as Treegator are helpful for young trees during heat waves. Fill the bag 2-3 times a week and your newly planted trees will fare the heat much better.
  • Mulch the root zone of trees to keep the soil cooler and reduce evaporation; 3-4 inches of mulch can do wonders for a heat-stressed tree, however, keep the mulch 6 inches away from the trunk to discourage fungal disease.
  • Make sure your irrigation system has been adjusted from the spring schedule

Click here for more information on caring for our urban tree canopy.

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Patricia Lombard
Patricia Lombard
Patricia Lombard is the publisher of the Larchmont Buzz. Patty lives with her family in Fremont Place. She has been active in neighborhood issues since moving here in 1989. Her pictorial history, "Larchmont" for Arcadia Press is available at Chevalier's Books.

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