Beat the Heat! How to Avoid Heat Stress in Plants

A heat wave has hit Southwest Montana in recent weeks. With near-record high temperatures blanketing our Valley, it is essential to find ways to keep cool. While we can beat the heat by enjoying recreational fun at the streams or the lake, our gardens and plants are not so lucky. When it gets hot, our plants get ‘stressed.’

Heat stress is often characterized by an extended period of time at which air or soil temperatures are hot enough to cause damage to plant function or development. Most plants grow best when temperatures range from 60 to 86 degrees F. Above this range, plant growth begins to slow and plant death can even occur. Soil surface temperatures often reach their peak in mid-August. As we approach this time of year, how can we identify heat stress in plants, and what can we do to prevent this?

There are several signs to look for in your garden to determine if your plants are suffering from heat stress:

• Leaf rolling and cupping
• Wilting
• Dry leaf edges
• Blossom and fruit drop
• Bolting (plants flower prematurely, before they would normally be harvested.)
• Sunscald (plant or fruit areas exposed to the sun during high temperatures become watery, discolored, blistered, or dried out.)

If you notice sign of heat stress in your garden, there are several techniques you can try to curb the effects of high temperatures.

One of the more basic solutions to reducing heat stress is ensuring your plants are receiving the water they need to thrive. In deciding the appropriate watering method, it is important to know you roots! For example, shallowly rooted plants or young plants with minimal root development will need to be watered more often, as they will dry out more quickly. Plants with a taproot or an extensive root system can draw water from deeper into the soil. This same strategy should be applied to plants that are in containers rather than garden beds, as their roots are restricted as well. In general, watering in morning, when the air is cool and wind is low, is also the most effective way for your plants to receive and retain water. This method reduces the potential evaporative loss that may occur later in the day.

Depending on the environment of your garden (ex. greenhouse, garden bed, etc.), providing additional humidity may also be helpful. Although leaf moisture can increase the potential for plant disease, in cases of prolonged high temperatures, the benefit of humidity likely outweighs the risk. Adding humidity to the system could be done by carrying out a light, overhead watering in the mornings, or using a mist sprayer to lightly coat the plants.

Mulch can also provide several benefits to plants in times of extreme temperature. The characteristics of mulch work like a type of protective barrier, shielding the soil from wind and sun. It can act as an insulator, keeping the soil cool in the summer, and conversely, preventing soil from losing heat in the winter. By blocking the soil from direct sunlight, it can also retain moisture better, allowing plants to uptake water for greater periods of time throughout the day. To receive the maximum benefits from mulch, Oregon State University Extension Service recommends spreading a 3-inch layer on top of your garden area.

We may not have control over temperatures or how much water we get, but when it comes down to it, there are things we can do to help our plants through the heat. To learn more about how to help your garden recover from, and prevent, heat stress visit: https://extension.oregonstate.edu/gardening/flowers-shrubs-trees/heat-wave-garden-how-identify-prevent-heat-stress-plants or talk to your local MSU extension office.