How to Prevent Heat Stress in Your Garden

Vegetables, Lawns, Trees, and Shrubs

Lawn problems

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Heat stress in plants is a real problem during July and August in much of the United States. Extended periods of high heat (particularly when the heat index soars over the 100-degree Fahrenheit mark) can take a real toll on your gardens.

Here are a few tips for helping plants through a hot, dry spell and keep them healthy and productive.

Vegetable Gardens

Vegetables need a reliable, steady water supply to stay productive. However, even with careful watering, your veggies may suffer from heat stress. The most common signs of heat stress in vegetables are sunburned foliage and fruits (usually yellow and crisp to the touch), blossom and fruit drop, and wilting. There are a few things you can do to help your vegetable garden through a prolonged hot spell:

  • Water regularly and deeply.
  • Mulch the soil with at least three inches of organic mulch to reduce moisture loss and help regulate soil temperature.
  • Shade certain crops, such as leafy greens and lettuces, to prevent them from going to seed, called bolting. They will bolt during periods of intense heat. However, providing some shade might offer a few more days before plant quality is diminished.

Lawns

Many lawns, including bluegrass, fescues, and ryegrass, naturally go dormant (turn brown and stop growing) during periods of high heat and drought. The easiest thing to do is just let nature take its course. Once temperatures return to normal, and the lawn starts receive adequate moisture, it will resume growth and green up again.

However, if this is not an option (due to homeowner association bylaws or other issues) you can keep your lawn green by providing at least one inch of water per week (up to two inches during high heat), delivered slowly and steadily.

Deep watering requires time; don't turn on the sprinkler and run it for only 20 minutes, that's not enough time to supply a deep drink. If the soil is very dry, chances are likely that most of the water you apply will simply run off or evaporate. Give the lawn a long, deep watering early in the morning so that the lawn is hydrated through the heat of the day. When you start seeing water running off onto your sidewalks, stop—you're just wasting water at that point. To accurately measure how much water has been applied, position a straight-sided glass or rain gauge that the sprinkler reaches to determine when one to two inches of water has been applied.

It would also help to stop mowing the lawn (it's not growing much in the heat anyway) so that you don't stress the lawn further.

Trees and Shrubs

Newly-planted trees and shrubs (less than two years since planting) can be hit particularly hard by heat and drought. Unlike lawns, young or mature trees and shrubs cannot go dormant during the growing season. To keep them alive and healthy:

  • Give them between two to four inches of water per week during very high temperatures (heat index above 100 degrees Fahrenheit) and drought.
  • To water trees and shrubs, a long, slow trickle is best. You might want to invest in a tree watering bag, which holds five gallons of water that slowly trickles out. A slow trickle enables water to soak slowly and deeply into the soil without running off ensuring that the water is reaching the root zone where it is needed.
  • Shrubs can be misted several times per day to increase the ambient moisture—this will prevent the foliage from drying out too much. Misting increases the humidity level and lowers the temperature around the plants.
Article Sources
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  1. Locher, Leann. “Heatwave in the Garden: How to Identify and Prevent Heat Stress in Plants.” Oregonstate.Edu, 25 June 2021, https://extension.oregonstate.edu/gardening/flowers-shrubs-trees/heatwave-garden-how-identify-prevent-heat-stress-plants.

  2. Tree and Shrub Watering Tips. University of Nebraska Lincoln Extension