Transpiration is the passive process that enables water to move up from the roots, through the branches, into the leaves and then out into the atmosphere. It not only helps deliver nutrients to the various parts of the plant but also helps to cool the plant. For transpiration to work, water is drawn up into the leaves, and these leaves have tiny holes in them called stomata.
These stomata open and close to help water evaporate, which in turn helps keep the plant cooler. During this process, the leaves also absorb carbon dioxide, which is required for photosynthesis. As you might imagine, plants with larger leaves have larger stomata, enabling more water to be released on hot days.
But, when it’s really hot, more water can get released through the stomata faster than it can be replenished, causing the leaves to get droopy on your plant. A good example of this would be hydrangea or hibiscus leaves. For plants with these large leaves, it’s not unusual for them to look pretty droopy at the end of a hot day even though there is plenty of water available for their roots.
In this case, the water replenishment will likely catch up overnight, and the plant will look fine in the morning. But here’s the interesting part: Only about 5% of the water being drawn up by the plant remains part of the plant. The rest exits the plant via the stomata.
But this remaining water helps maintain plant rigidity. For an example of this, if you have a hydrangea or hibiscus, go out and feel those l.