Heat islands: tropical paradise or slow death for trees?
We’ve all seen it, but most of us don’t understand what it means. Naked upper branches of trees, singed leaves, neighborhood shrubs struggling to survive, our own garden and landscape plants growing less well than expected are all signs of heat island effect.
What are heat islands?
The term ‘heat islands’ refers to land that used to be soil, bushes, and trees, and is now concrete, asphalt, and buildings. Before all that development, natural cycles and the permeability of the soil kept things cooler and healthier for plants. All the impervious, manmade materials that now cover up 3% of the earth’s landmass absorb heat, creating a zone of higher temperatures called heat islands.
Do I have heat islands?
Unless you live in a tent in the wilderness, yes, you have heat islands. Driveways, patios, extended foundations, concrete paths and walkways, roofs, sidewalks, and the street in front of your home can all create their own heat islands.
How do heat islands impact landscape plants?
Plants installed in or near heat islands must contend with soil temperatures that can be 50 to 90° hotter than the air. This means, on a scorching California summer day, when the air is 95°F, your plants’ roots may be struggling to survive temperatures as high as 185°F! All this strain takes its toll. Most trees reach what is called a ’thermal death threshold’ at 115°F. Held too long at temperatures above this point and even the healthiest tree can die. Even if they survive, plants growing in heat islands have significantly shorter lifespans and are more susceptible to pests and disease. Also, things don’t cool down for these plants as the sun sets. While we may enjoy the lower temperatures of evening, concrete and asphalt hang on to all that absorbed heat, slowly releasing it into the immediate area, making evenings the hottest part of your plants’ day.
Impact of heat islands on water use
Plants growing in heat islands need as much as 50% more water than the same plants grown elsewhere. Since a mature tree can use up to 250 gallons of water a day during the peak of summer, that percentage can translate into a lot of water! Also, if you re growing edibles, such as cucumbers, peppers, lettuce, broccoli, or cauliflower, in a heat island, the stress can cause these foods to turn bitter, or bolt.
How can you help plants in heat islands?
City managers are working toward reducing the heat island effect and you can. too! Use these tips to help your plants survive the heat island effect:
Since plants that are growing in heat islands are already under a lot of stress, be sure to monitor for pests and diseases regularly, so that you can apply treatments right away, before things get out of hand.
Reducing heat islands on your property
There are many steps you can take to reduce the number of heat islands on your property. Not only will this help your plants to be healthier, it also reduces energy bills (if you use A/C), water consumption, and emissions from energy production. Here are just a few of the ways you can reduce the number of heat islands on your property:
Help your plants and the environment by eliminating heat islands around your home.
You can grow a surprising amount of food in your own yard. Ask me how!
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