Written By Lara Wadsworth

Summer is here, and the heat is turning up. As the sun becomes more intense and daytime temperatures routinely soar, some plants struggle to cope. Sunburn, sunscald, leaf scorch, and heat stress are common problems that plants can experience in extended periods of high heat conditions. The good news is that you aren’t helpless! There are several practical steps you can take to give your garden the best chance, even in the hottest growing zones.

Understanding the Signs of Heat Stress

Heat stress can manifest differently depending on the plant and the specific cause (aside from the heat). However, if you are noticing wilting during the day (even after watering), widespread browning or drying on the edges of leaves, lots of yellowing leaves, leaves uncharacteristically dropping, distinct brown patches on the top side of leaves, abnormally slow growth, or dry, crispy soil, you should continue reading. These are some of the symptoms of heat stress. The best course of action is to use the following tactics to avoid crop loss or reduce the effects of the summer heat.

How to Protect Plants from Heat Stress

There are many ways to reduce the effects of the summer heat on your garden crops. When deciding what to try in your garden, consider the needs of your plants. Are they getting enough water? Is the soil retaining the water you give it? Are you growing the right type of plants at the right time? The most important tasks in the garden are the ones that support the basic needs of your plants. Once those are met, additional actions can be considered to improve yields, flavor, and appearance.

Water Wisely

One of the leading causes of heat stress is when the plant is unable to take up water properly. Give your plants the best chance by watering early in the morning or late in the evening. Watering in the middle of the day increases the amount of water that will evaporate rather than be available to the plant.

When watering perennials and woody plants, water deeply. It is better to water deeply and infrequently rather than frequently and shallowly. This concept again goes back to evaporation. You want the water to reach the roots of the plants and stay there, rather than just wetting the top of the soil. As the soil dries between water applications, the roots will be forced to work their way deeper into the soil in search of water. Water directly at the roots as much as possible and really soak it.

Provide Shade

Another great way to protect plants from intense midday heat is to use shade cloths, garden umbrellas, or old bed sheets strung up between stakes. You don’t want to prevent the plants from getting any sun, but giving them a bit of cover to mitigate the intensity of the harshest sun of the day can go a long way. There are numerous DIY options available. The sun is at its most intense between noon and 3 pm each day. For potted plants, you can temporarily relocate them to a shadier spot. Putting them on caster wheels can help with this if it is a common occurrence.

Use Mulch

Mulch is a fantastic way to keep the soil temperature more stable, reduce excess water evaporation, and improve the plant’s ability to uptake as much water as it needs. You can use anything like straw, bark, leaves, wood chips, and pebbles. I recommend using a light-colored mulch and avoiding dark ones (more on this below). When you apply, aim for a thickness of at least 2-3 inches to be effective. Bonus points because mulch will also reduce weeds, thereby reducing competition for precious water.

Boost Humidity

A simple way to reduce heat stress is to mist the plants. The extra humidity in the air can help plants to take in more water through their stomata and reduce the temperature on the leaf surface. Oregon State University Extension says, “Typically, applying moisture to leaves intentionally is not recommended in the garden: leaf moisture, along with the presence of a pathogen and the right temperature, increases susceptibility to plant disease. However, in cases of prolonged high temperatures, the benefit of a humid environment probably outweighs the risk of plant disease.”

Prioritize Soil Health

Healthy soil is the key to a healthy plant, regardless of the temperature. Regularly apply high-quality compost to your soil and avoid over-fertilizing with synthetic options. Avoid fertilizing during extreme heat and use diluted fertilizer if needed. If you must use fertilizer (versus compost or compost tea), consider slow-release options. Healthy soil is better at retaining moisture and keeps roots cooler. Add compost or organic matter regularly and consider using water-retentive mixes such as the Max Water Retention Soil Mix for potted plants.

Choose the Right Colors

Dark colors absorb more sunlight and get warmer, faster. Gardeners in cooler zones use dark-colored landscaping fabric to help warm the soil earlier in the season. However, in the south, where heat stress is a risk, it is best to avoid dark colors on the soil whenever possible. Choose lighter-colored mulches like straw and wood chips to reduce the temperature of the soil. If you’re using containers, use light colored options like white or light tan. Additionally, group pots together for mutual shade and humidity.

Avoid Hot Hardscapes

Avoid putting containers on hot patios or concrete. Rock, stone, and cement-like materials absorb heat and retain it a lot longer than grass and dirt. Avoid having your garden beds near these types of hardscapes when at all possible. You garden will be cooler overall without these elements nearby. If you must locate your pots or garden near hardscapes, utilize the shade trick we talked about above and try to shade the hardscapes to overall reduce their heat retention.

Grow Heat-Tolerant Varieties

If you are consistently having problems with heat stress, it is a good idea to focus on growing plants that are heat-tolerant. There are entire species that are more suited to hot temperatures than others, such as peppers, melons, and zinnias, but you can also find lots of varieties of other species that have been bred to be heat-tolerant. For example, lettuce famously hates heat, but there are some varieties such as Black Seeded Simpson and Ruby Red that handle the heat much better than other types. Do some research about heat-tolerant varieties of the plants you want to grow, and you’ll likely have better success in conjunction with these other tips.

To get the most out of your garden, strategically plan ahead to grow cool-season plants during the shoulder seasons. This will often result in a healthier and sweeter harvest for crops like leafy greens and root crops. Warm season crops will naturally perform better against the hot summer temperatures. For more information about what crops are best grown during the summer, checkout our article about heat-tolerant vegetables.

Quick Summer Gardening Tips

Don't plant or transplant anything if temperatures are extreme.

Don’t prune trees or shrubs during extreme heat.

Don’t apply any kind of herbicide or pesticide (or any kind of chemical) in temperatures above 80 F.

Take care of yourself in high heat too! Drink lots of water, use a wide-brimmed sunhat, wear light colored clothes in breathable fabrics, and take frequent breaks in the shade.

Heat can be stressful for humans and plants, but it doesn’t have to be the end of gardening for a while. Unlike cold, heat won’t necessarily kill a plant; it may just slow it down. Use these strategies, such as improving soil health, mulching, increasing humidity, and providing shade, to get your plants through the hottest time of the year so they can keep producing beauty and/or food for you to enjoy. Throughout all of these strategies, don’t forget to observe your plants closely and respond accordingly. Oftentimes, it takes a lot of practice and a few failed plants to get a handle on something like heat stress. Contact your local extension office for more specific details of what works for your local area.

Lara Wadsworth, True Leaf Market Writer

I am a native of Southwestern Michigan, where I currently reside. I love all things plants! After completing a Bachelor's Degree in Horticulture, I found a dream work-from-home job that allows me to share my passion. Now, I spend my days writing for TLM, playing with my dog, eating delicious food with my husband, and plotting my next landscape or gardening move. I believe everyone should get down and dirty in the soil now and then. Happy Gardening!