One thing I love about working in the horticulture world is that there is always something new to learn or observe about plants. The hot, dry summer we are experiencing makes for an interesting time to learn about plants, although I would prefer to have cooler temperatures and rain!
Plants require water for survival, something we are all acutely aware of during a Texas summer. When it gets dry, plants have very different responses for surviving a lack of water. Generally speaking, plants have three strategies to survive drought
conditions: drought avoidance, desiccation tolerance, and drought tolerance.
Drought avoidance is a very interesting strategy used by many plants. Heat and drought can cause dehydration in some plants, so they will close their stomata in the leaves during the day to reduce evapotranspiration. Stomata will open at night to collect carbon dioxide so they can complete photosynthesis processes during the day.
Other plants will drop leaves to avoid drought. Leaves require a lot of energy and resources, so some plants will drop the leaves to conserve resources. Some plants go so far as to curl up and die, leaving their seeds to carry on the family name when conditions are better.
The second strategy is desiccation tolerance when a plant will stop metabolic activity as a result of low cellular water content. Desiccation means the plant gets completely dried out. The plant can recover from this dehydration when water is available. If you have ever been to Gorman Falls at Colorado Bend State Park or walked along the trail near Booty Road Park, you might have noticed the ferns and moss along the waterfalls. During drought, the ferns and moss dry out (and appear to be very dead), but they perk right back up when water is available.
The final strategy is drought tolerance. Some plants are just better at surviving drought because of their structure. Some plants might have thick, leathery leaves with waxy cuticles that cut down on water loss and reflect heat away from the plant. Other plants have small, thin leaves that reduce the surface area from which water can be lost. Some plants, like pine needles, have sunken stomata pits which trap moist air. Other plants have hairy leaves which shade the stomata and protect plants from extreme temperatures and light. Lamb’s ear is a good example of a hairy leaf.
Take a look around your landscape this week to observe all the different strategies that plants use to survive drought. Some plants use more than one strategy! You might notice that St. Augustine grass has waxy leaves that help it tolerate drought, and it will turn brown when it gets dry for too long. It comes right back after a good rain. Or take a look at marigolds that completely dry out but have lots of seed in each flower that will spread next year for another round of beautiful blooms.
Drought is tough on plants, and maybe just as hard on us to endure, but it is amazing to see how plants have adapted strategies to survive dry times until the next rain.
For more information about trees or other lawn and garden topics, contact County Extension Horticulturist Kate Whitney-Hajda at the Williamson County AgriLife Extension Office at 512-943-3300.
