In this heat, it seems like no matter how much I water some of my plants, they get wilted and droopy during the heat of the day. What am I doing wrong? CH

This heat has been taking a toll on our plants and us. Wilted leaves on your plants this time of year are typically a symptom of one or two things, both of which are related to water.

Plants use water to transport nutrients throughout the plant. As we know, water is absorbed into the plants through the root system. It is then drawn up into the plant along with nutrients that nourish the plant.

Plant leaves have tiny holes called stomata that open and close to allow water to evaporate out of their leaves, helping keep the plant cool through a process called transpiration. During transpiration, the leaves also absorb carbon dioxide which is essential for the process of photosynthesis.

When it’s really hot, plants with large leaves such as hydrangea or cucumbers can have a hard time drawing up enough water fast enough to keep up with the water being lost through this process. When this happens the leaves wilt.

Also, plants with big leaves tend to have larger stomata which makes it easier for them to suffer from dehydration or water-deficit stress. Plants that tend to have smaller stomata are better able to regulate this exchange of gasses making them not as susceptible to dehydration.

Interestingly, only about 5% of the water that is absorbed remains in the plant. But this water is important for maintaining plant structure by what is known as turgor, which is a term related to plant cell rigidity. This rigidity helps keep the plants upright and able to support themselves. If you’ve seen a plant that is droopy and leaning over when dry and then after watering it’s standing straight and looking like it should, the plant has had its turgor restored.

Ironically, dehydration can also occur in plants that receive too much water. Healthy garden soil is about 25% open spaces filled with air. Oxygen is necessary to help roots absorb water. If the soil gets saturated, driving out the oxygen in the open spaces, the roots will not be able to absorb the water. As a result, many a gardener has overwatered their plants after seeing droopy leaves thinking the plant needs more water which unfortunately contributes to further decline in the plant. Roots that remain waterlogged for a period of time are susceptible to a condition called root rot which can ultimately kill a healthy plant.

So, if your plants look droopy in the afternoon but have recovered by morning, they are likely just releasing water at a faster rate than they can absorb. However, if they remain dehydrated in the morning, it’s time to increase the amount of water you are putting on your plants. There are a variety of inexpensive water moisture meters available if you would like to be able to measure the moisture levels in your soil. Good luck.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701, dropping by our Diagnostic Center at 4116 E. 15th Street, or by emailing us at mg@tulsamastergardeners.org. Photo: John Ruter, University of Georgia, Bugwood.org