Identifying Plant Heat Stress: How to Protect Your Garden During a Heat Wave

When the sun is scalding and the humidity is high, humans and animals aren’t the only ones feeling the heat. When temperatures reach 85 degrees Fahrenheit or higher for extended periods of time, plant growth starts to slow—and they may show visible signs of stress.

Dealing with the heat is tough enough without having to worry about how your favorite rose bush or zucchini plants will fare. But don't worry: Here’s how to spot heat stress in your plants and what you can do to help them beat the heat.

What Is Plant Heat Stress?

Most plants grow best in temperatures that stay between 60 and 85 degrees Fahrenheit. When confronted with long stretches of extreme heat, plants may show signs of heat stress such as scalding, bleaching, drying, and other damage. While heat stress is not a death sentence, it’s important to intervene if you suspect your plants are experiencing it. Keep in mind that some desert plant varieties, like succulents and cacti, are much less likely to undergo heat stress.

Identifying Heat Stress in Your Plants  

Our plants can’t tell us when they’re in trouble, so how do you know if your plant is overheating? You can usually spot heat stress through these telltale signs:

• Wilting

• Dried-out leaf edges

• Leaf cupping and rolling

• Premature blossom and fruit drop

• Heat cracking in fruits

• Blisters

• Bleached areas

• Browning

9 Ways to Protect Plants During a Heat Wave

The best thing you can do to combat plant heat stress is to intervene ASAP, so it’s important to act fast once temperatures rise. If you need help identifying plant heat stress or determining the best course of action for your garden, contact a local gardener to get a professional opinion. 

Here are the best ways to protect your plants when the weather is too hot for you or your plants to bear.

Be Mindful of Your Watering Time

The hot afternoon sun will quickly evaporate water from the soil, so it’s best to water your plants before 10 a.m. (This method is also a helpful way to conserve water!) You can opt to water at sunset, though it’s best to check on your plants in the morning and water more if needed.

Watering late in the evening is a no-go, as this may attract ravenous nighttime insects and leave your plants vulnerable to fungi.

Monitor Soil Moisture Levels

Watering is the most important step in preventing (and addressing) heat stress. While sticking to your regular watering regime, pay close attention to the moisture level in the soil around your plants. If you spot cracking or other signs of dried-out soil, give your leafy friends an additional drink to help them beat the heat.

"On the other hand, if the soil still has moisture in the first top two inches, there’s no need to water right away,” says Tara Dudley, owner of Plant Life Designs.

Mulch Your Garden

Mulching your garden can be highly beneficial, especially for preventing heat stress. Not only will it help retain moisture in the soil, but it will also provide a protective layer against the scalding heat. As a bonus, it can also help control pesky weeds around your garden. 

Choose Heat-Hardy Plant Varieties

If you live in a warm-weather climate and your garden experiences a lot of heat stress during the summer, consider cultivating more heat-resistant varieties. Succulents are a great choice, but they’re not the only option if you enjoy more colorful and leafy plants. "Plants that are native to your area are always a great option as well," Dudley said.

Here are some beautiful, vibrant florals that can stand up to serious heat: 

• Marigold

• Geranium

• Caladium

• Cosmos

• Egyptian Star Flower

• Lantana

• Lemon Verbena

• Salvia

• Sedum

Time Your Plantings Right

Cool-season plants such as kale and broccoli are among the most vulnerable to heat stress, so it’s important to maintain a planting calendar and time your plantings right. If you’re planting from seeds, follow the instructions on the packet.

Don’t Wait Too Long to Transplant

If you’re starting a crop of seed babies indoors, the best time to transplant garden plants is usually in the spring—right after the danger of frost passes. If you wait too long to transplant them into the garden, you could end up killing your seedlings, as they’ll be too weak to stand up against the extreme heat.

Avoid Pruning Sun-Damaged Leaves

While they’re not much to look at, those brown, shriveled, or sun-fried leaves have the important job of shading new growths underneath them. Resist pruning away sun-damaged leaves until the heat wave has passed.

Move Potted Plants out of the Sun

Extreme heat is one situation where having a container garden comes in handy. If you spot your potted plants struggling, move them to a shadier spot in your yard until the temperature cools down. You can even bring them inside if you have a spot for the pots near a bright window. 

Consider Options for Plant Sun Protection

If the sun is at its worst and you can’t move your plants, you’re not powerless. Bring the shade to your garden with a shade cover, such as a shade cloth, floating row covers, or an umbrella. In a pinch, you can also use a bed sheet or window screen. Place wooden stakes around the area and drape your covering over to give your plants some much-needed shade.

Will Plants Recover From Heat Stress?

If your plants suffer major heat trauma, there’s still a good chance they’ll bounce back. If possible, move the plants into the shade or inside. You’ll only need to keep them there until the extreme heat subsides.

Next, give the plants a deep watering and allow the soil to dry out before giving them another drink. Avoid keeping the soil soaked constantly, as this can lead to root rot (a more severe and life-threatening situation for your plants). You should also skip the fertilizer until the heatwave passes—new growths will be especially sensitive to harsh sunlight.