Expert Advice on Protecting Your Plants From Extreme Heat

3 Critical Symptoms, 4 Solutions, and 9 Plants That Tolerate Heat

If you aren’t prepared, plant loss due to heat stress can occur this summer. We’ve compiled the best advice from Gardeners’ Guild experts and the University of California on protecting your plants from extreme heat.

Our post is a simple guide to the causes of heat stress, its symptoms, and solutions. It also includes photos of plants that can tolerate high temperatures.

How Extreme Heat Causes Plant Stress

The ideal growing temperatures for a plant are between 60 to 80 degrees. However, once temperatures reach 85 degrees and over, the risk of heat stress multiplies exponentially.

Why? A simple reason. A plant’s ability to regulate its temperature diminishes when temperatures rise above 85 degrees during extreme heat.

How a plant cools itself

Water evaporates through the pores in its leaves, a process called transpiration. But when it loses too much water, the pores close, and the plant no longer has the energy to do that. It gradually starves because it has exhausted its food reserves.

Not unlike human beings. We know what it’s like to feel dehydrated. It depletes our energy reserves. You probably have a story about what it’s like to have heat stress.

Starving plants are vulnerable to pest infestations, and photosynthesis, converting sunlight into energy, decreases. If heat stress continues for an extended time, the plant’s growth will be stunted, and its health will decline. The graphic below illustrates the progression of heat damage.

Even those who can tolerate high temperatures may also suffer from heat stress. It can occur when nighttime temperatures do not cool enough, or the soil becomes too dry and hot during a severe and prolonged heat wave.

Symptoms of heat stress in plants

 

3 Solutions to Protect Plants from Extreme Heat

1. Watering the right way

Give your plants a good soaking. Water slowly and deeply to encourage deep root growth. Before a heat wave. Drip irrigation is ideal because it dispenses water slowly and goes directly to the plant’s roots.

Water early in the morning, but don’t overwater. Too much water can cause reverse damage. Use a soil moisture sensor to ensure your plants are getting enough moisture.

2. Mulch

Master Gardeners advise a three to four-inch layer of mulch around your plants. Mulch has many advantages, including helping keep plant roots cool and retaining moisture.

3. Shade cloths or umbrellas

This cools the soil and blocks the harmful sun’s rays. Depending on the size and location of your garden, a beach umbrella or, better yet, any unused umbrella will work!

Shade cloths are lightweight and have microscopic holes to allow light and water to permeate. Depending on the light they let in, you can purchase them in various densities or use material on hand, such as bed sheets or window screens.

Your shade cloth must be high enough, at least 2 to 3 feet above your plants, so it has enough ventilation. Multiple options for securing it exist, from trellises to pergolas and plant stakes. They can be as simple or sophisticated as you like.

Securing the cloth on one side of the plant should be sufficient to block the most harmful sun rays.

4. How to protect your container plants

Group your container plants. This will create an individual microclimate that retains moisture and stabilizes temperature fluctuations. Move them to shady locations and check them twice a day.

Can Plants Recover from Extreme Heat Stress?

Yes, they can. There’s no simple answer. It will depend on a few factors.

• The severity of the heat.
• Plant type.
• Maturity: Plants near the end of their useful lifespan may not survive.
• The plant’s health before the heat wave.

We urge you to contact a professional if you notice a heat-stressed tree. They are the most expensive to replace and can be a safety hazard if infected.

Don’t fertilize during a heat wave.

Fertilization requires that the plant expend energy to absorb it. However, during extreme heat, plants’ energy is limited due to the stress of the heat.

Don’t prune (or only if necessary)

A plant needs energy to recover from the shock of pruning, but during a heat wave, its resources to recover may be severely depleted. Pruning can stimulate new growth, but a plant struggling during a heat wave may lose precious water resources and become severely dehydrated. Open wounds can become entry points for pests.

Don’t remove damaged foliage.

This may seem counter-intuitive, but the foliage can provide some measure of protection from the sun’s rays.

Don’t water when the sun is at its highest point.

It’s a waste of water. It will evaporate before you finish reading this one sentence.

Pay Special Attention to

Plants near pavement may need protection from extreme heat

At 3:30 in the afternoon of a typical summer day when the air is 84°, the pavement can heat up to 142°. Any plants along walkways, patios, or steps are at risk of being impacted by the radiant heat from the pavement.

Young plants

Just like babies, they have fewer energy reserves to withstand extreme heat. Their shallow root systems also make them less able to absorb water. Protect them by closely monitoring and ensuring they have enough water and shade.

Fruiting plants

They’re vulnerable and should be monitored regularly. Fruit may drop too early, affecting the quantity and quality of the fruit. They need sufficient deep watering, shade, and mulch.

About trees

On a hot day, a mature tree can lose several hundred gallons of water through its leaves. As said above, enlist the help of a professional. They can give you reliable solutions to protect them from extreme heat.

9 Heat-Tolerant Plants

Below is a sampling of perennials that can tolerate heat. Keep in mind that any plant will show signs of heat stress at 90 degrees. Its ability to recover depends on the treatment and the length of the heat wave.

 

 

6 Edibles That Can Cope Include

• Tomatoes
• Squash
• Cucumbers
• Sweet potatoes
• Rosemary (although keep in mind this is a fire hazard)
• Basil

Closing thoughts

Like most gardeners, I beam with pride when my plants look happy and am concerned if they look stressed. Writing this post was a good reminder of how to better care for them during our ever-increasing and longer heat waves.

Remember these key points when caring for plants during extreme heat.

• Water the right way. (see tips listed above).
• Pay special attention to trees, young plants, and plants in containers.
• Shade cloth is a good tool to help minimize damage from heat stress.

Every plant is vulnerable to heat stress during a prolonged extreme heat event, but with these tools, you can boost their chances of survival.