6 Signs of Plant Heat Stress

6 Signs of Plant Heat Stress

I wrote a previous post about keeping yourself safe while gardening in hot weather, but what about your plants? A heat wave can put a lot of stress on the plants in your garden too. Here are a few signs of garden heat stress and how to deal with them.

1. Overwatering

Heat is not the same as drought. When temperatures reach into the nineties and higher, some plants will begin to wilt regardless of how much moisture is in the soil. Avoid the temptation to over water! The heat is bad enough…too much water can lead to fungal diseases. Instead, you should be sure that you provide enough water to maintain the proper soil moisture level. Also refresh mulch that may have degraded: a three inch layer of mulch over the root zone will insulate the roots against the heat and minimize moisture loss through evaporation. A well cared-for plant will perk back up as the sun goes down.

6 Signs of Plant Heat Stress
Pepper plant with previous leaf drop. As the temps cool down, the plant is recovering with new leaf growth.

2. Leaf Drop

Many plants, from trees to annual flowers, will drop a significant number of leaves when they are heat stressed. In this case, be sure to check the water situation. Water if needed and wait for the heat to subside. Sometimes leaf drop occurs as a response to drought, other times it happens as a response to intense heat when the plant can’t uptake the existing water fast enough to support the entire canopy (see the paragraph above).

6 Signs of Plant Heat Stress
Pepper plant with no flowers or fruit.

3. Flowers And Heat

Some plants may stop flowering in hot weather. Tomatoes and peppers fall into this category. They may simply drop their flowers without developing fruit, or possibly not flower at all until temperatures cool. If you live in an area that consistently experiences extreme heat in Summer, choosing the varieties best adapted to hot weather and plant them extra early to ensure a crop comes in before the really hot weather arrives.

6 Signs of Plant Heat Stress
Lettuce bolting in the heat.

4. Bolting

Cool weather crops, like spinach and cabbage, will “bolt” in hot weather. Simply put, the heat signals the end of their life span, which culminates in flowering and seed production. Not much is to be done to stop a plant that bolts, so you may wish to harvest and use these plants before the flavor is ruined by the bolting process.

6 Signs of Plant Heat Stress
Blossom end rot.

5. Blossom End Rot

Tomatoes, peppers, squash and cucumbers may exhibit black spots on their bottoms in hot weather. Blossom end rot is caused by a calcium deficiency. The calcium deficiency is caused, more often than not, by inconsistent soil moisture. The best response to this problem is to water deeply and mulch well. These steps will help you avoid the wet/dry cycle that is the leading cause of blossom end rot.

6 Signs of Plant Heat Stress
Parsley with sunburned leaves.

6. Sunburn

Yes, plants (and fruits) may get sunburned just like people do. This often happens  when a newly installed plant gets shocked by either sudden sun exposure or heat that is more intense than it experienced in it’s nursery location. Minimize the chance of sunburn by properly hardening off plants before planting them into their permanent home. Also, if the heat is really intense, it may be beneficial to provide a temporary shade over the plant as an extra layer of protection.

Gardening in extreme heat should revolve around minimizing heat stress for both you and the plants. Stick to watering and mulching as needed, and do it early or late in the day. Stay cool.

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