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Having worked at Louisiana Nursery for many years, both on the lot and inside the office, I have seen my fair share of heat-stressed plants. Even with morning sprinklers and multiple hand waterings per day, some plants end up dropping their leaves. In Louisiana summers, all the negative effects feel like they’ve been put under a magnifying glass. We’ve grown accustomed to hearing about record-breaking temperatures, but the last few years have been truly brutal for both people and the landscape. We are all taking precautionary measures: drinking more water, limiting physical activity, and staying in the shade or indoors whenever possible. But who takes care of our poor plants?
First: What is heat stress and why is it a problem? Gardeners typically encounter two different forms of direct heat damage: UV damage and heat-induced wilting. UV damage is like the tissue damage we suffer on our skin, meaning leaves can burn from too much direct sunlight. Yellowed, dry leaves are a common indicator of UV damage. Even without much direct sunlight, extreme temperatures will cause heat stress in your plants. Although it is a small difference, you will usually see the leaves turn pale green instead of yellow. You may also notice a wilted or tired appearance to the plant body. Either way, prolonged periods of heat stress will cause leaves to drop and plants will go dormant to protect themselves. If left unchecked, chronic heat stress can develop, leaving an unproductive or dead plant.
Indirect effects, in my opinion, tend to be the main culprit in the actual death of a plant. For example, a large 10 to 15 year old shrub will have survived countless diseases and insect infestations throughout its life. While these are not beneficial, the shrub will likely recover without much trouble. However, when the plant is already weakened by chronic heat stress, insects or disease may be what pushes it over the edge.
As is often the case in gardening, prevention is the easiest way to keep your plants happy and healthy. We use preventive measures for weeds, diseases, fungi and insect infestations. The same principle applies at extremely high temperatures. The first and most obvious step you should take is to change your watering habits. Being aware of when temperatures reach 90 degrees or higher and adjusting sprinkler schedules or hand watering schedules may be enough to fully cope with hot summers.
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Another good practice is to properly cover all your plants, even those in pots. Mulching provides two major benefits in this scenario: moisture retention and direct UV protection. You’re already watering earlier in the day and more deeply than before. Mulching increases these efforts by retaining those deep waterings for longer. As for direct protection, the idea is simple: mulch is an additional barrier between your plants’ delicate root system and the sun’s harsh rays. I can say from experience that – even with careful and regular watering – the sun’s rays will damage the roots through bare soil. At the very least, it keeps the soil temperature in a much more comfortable range for the roots.
Another preventive measure I follow also has to do with the roots: applying a root-stimulating hormone. This is not something that can take effect as immediately as mulch, but products like Ferti-lome root stimulator really work wonders. It will help your plants develop a larger, more vigorous root system in a shorter period of time. I planted a linden tree in early spring last year. Between a heavy application of mulch and multiple applications of root stimulator, I didn’t see a single yellow leaf even during the hottest stretches of last summer. I was also able to keep my watering schedule relatively low maintenance, two to three times a week. This watering, combined with rooting hormones and careful inspections for diseases and non-beneficial insects, will give your plants the best chance to survive and thrive in warmer conditions.
If my lime tree had still been somewhat stressed, my last preventive resource would have been the simple but effective shade cloth/cover. This works best if you can give your plants full sun in the morning and shade on scorching afternoons, but bringing plants in before work will help more than hurt. For potted plants, place them under the patio to reduce direct sunlight. Just remember that your plants still need sunlight to grow, and it should only be used during the especially brutal days of summer. In 2024, that could last weeks instead of days.
If your plants are already suffering from heat stress, you have some tough decisions to make. For citrus trees and woody shrubs, it can be as simple as removing dried, burned leaves and continuing a vigorous care routine. In the case of garden flowers and herbaceous plants in general, the damage has probably already been done. Each plant is different; Deep watering to compensate for harsh conditions may work for some but be detrimental for others. This is just another reminder that being aware of the weather and your plants’ needs ahead of time will prevent wasting energy on useless projects. If you are determined to help your plants recover, your best option is to use shade cloth or patio to reduce the amount of direct sun. Whatever you do, do not prune or trim your plants during this time. You may be surprised in the fall when that green growth begins to return.
We could consider the last few years an aberration, the hottest we’ve ever seen. But, if trends continue in the direction of the last decade, it could be the coolest summer for the rest of our lives! Either way, paying close attention to the weather and weather patterns will make you a more successful gardener. That can mean more time in the sprinklers, or even completely different plants.
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