By Heather Kirk-Ballard

LSU AgCenter Horticulturist

It’s beginning to look like fall all around us as plants go into survival mode during this heat wave. Temperatures continue to soar, and the rain is nowhere to be found. Plants have several strategies to survive during droughts and cope with heat stress, both of which are conditions of water scarcity and high temperatures.

You will notice many trees right now with yellowing and browning leaves. Some trees have dropped their leaves altogether. This is survival mode. In addition, heat stress can lead to the browning or scorching of leaf edges and surfaces. This is often due to the disruption of regular cellular processes caused by extreme temperatures.

Plants and trees cool themselves through the process of transpiration. With no water, they have stopped transpiring to limit water loss, and many are going into an early dormancy and dropping their leaves. This state of dormancy means plants and trees reduce or stop their growth processes until more favorable conditions return.

If you have a vegetable garden, you may have noticed reduced flowering and fruit set. The high temperatures can disrupt flower formation and fruit development, and you may have seen vegetables and fruit trees dropping fruit or flowers. This will lead to reduced yields in many crops.

Excessive heat can negatively impact photosynthesis, the process by which plants produce food from sunlight. This can result in reduced plant health. It's important to note that different plant species exhibit different degrees of tolerance to drought and heat stress, and the severity of these signs can vary.

So, what can we do during this time? And what should we not do?

To do:

1. Water plants at the proper times and for adequate lengths of time in parishes where it is allowed. The early morning between 2 a.m. and 6 a.m. is the best time to water followed by late in the evening after the sun has gone down. This reduces evaporation. Slow, deep watering is the best. Excessively dry soil becomes hydrophobic and actually repels water. Water flowing at a fast rate will just run off, so a slow drip or rate will be best to allow the water to go down into the soil.

2. Shade plants where you can. Shade can reduce the temperatures and sun exposure to plants that are scorching.

3. Mulch the root zone to help reduce evaporation of water from the soil and to help moderate root temperatures. Mulch can keep soil cooler in the summer and warmer in the winter.

4. Raise your lawn mower blade or skip the mowing all together. Stressed lawns will be further stressed by mowing. Take this time to instead water lawns very early in the morning.

5. Make note of any plants that are doing well during this time. This will be a great future reference for selection of plants to use when replacing those that do not survive this summer’s unexpected heat and drought.

What not to do:

1. Do not cause any additional stress to plants. Heavy pruning is not suggested during this time. Until we have a significant amount of rain and reduced temperatures, we will not know the full extent of how plants have been damaged. Once plants begin to leaf out again, you will notice the portions of the plant that did not survive, and you can prune those out then.

2. Do not fertilize any plants during this time. Fertilizer encourages growth, and without water to support that growth, it will cause further stress and damage roots and plant tissues. This will harm the plant’s health. In addition, because very dry soils are hydrophobic and repel water, those fertilizers are more likely to run off and end up in nearby bodies of water, causing pollution.

3. Do not use herbicides on the lawn during hot temperatures. Weeds, especially those that can tolerate drought, can take over when turfgrasses are under stress. Do not be tempted to apply herbicides that can further injure the lawn. Instead, hand pull weeds or mechanically remove them.

Proper watering practices, shading, mulching and selecting heat-tolerant plant varieties are some of the strategies that gardeners and farmers can employ to mitigate the effects of drought and heat stress on plants. Right now, the best thing to do is water where you can and hold off on most activities in the garden.

Raise mower blades or avoid mowing altogether during drought to prevent further stress to lawns. Photo by Heather Kirk-Ballard/LSU AgCenter

Many plants are curling their leaves in an attempt to reduce their exposure to the sun and limit water loss through transpiration. Photo by Heather Kirk-Ballard/LSU AgCenter

Water early in the morning or late in the evening with soaker hoses at the base of plants to reduce water evaporation. Photo by Heather Kirk-Ballard/LSU AgCenter

Wilted plants show signs of lacking the water necessary for healthy growth. Photo by Heather Kirk-Ballard/LSU AgCenter