By Cindy Robertson, Extension Master Gardener
Drought conditions can wreak havoc on gardens, landscapes, and trees, leaving many homeowners worried about the fate of their beloved flora. This past year exhibited longer than average dry periods. Northern Virginia has experienced moderate drought and remains under a drought watch at the time of this writing,[1] with severe drought persisting elsewhere in the state.[2] Climate change will aggravate drought conditions in the future.
Under proper care, including eco-friendly water use, gardens may remain fresh and healthy during drought conditions. Even so, life sometimes sidetracks the most diligent of gardeners, leaving our good intentions occasionally as dried up as our trees and plants.
In this article, we will explore the signs of drought stress in trees and plants, how to assess their chances of recovery, and what steps can be taken to aid in their revival. These tips should enable you to better understand and prevent drought stress as well as encourage patience if your trees or plants are recovering from drought.
Identifying Drought Stress in Trees and Plants
Wilting and Drooping Foliage: One of the most visible signs of drought stress is wilting or drooping leaves. This occurs as the plant loses water faster than it can absorb it. This dogwood tree (Benthamidia florida) shows signs of drought stress with its wilted leaves.
Temporary Wilting: As the name suggests, this wilting occurs only during the day. Leaves are able to recover and appear normal the next morning.
Permanent Wilting: Persistent drought conditions may produce wilting that remains even in the early morning. Some plants may suffer permanent damage or even death while others may survive or at least partly recover
Photo: Missouri Botanical Gardens
Crisp, Brittle Leaves: Drought-stressed trees may develop leaves that become dry, crisp, and easily crumble. This kousa dogwood (Cornus kousa) developed crispy leaves during late summer due to an extended period of no rainfall and extreme heat.
Note that the yellow variegated shrubs behind the tree seem unaffected by drought stress, revealing that not all plants will react similarly to drought. Trees and other plants in sunny or sloped locations, with more opportunities for water loss, may show greater signs of stress.
Yellowing or Browning of Leaves: When a plant experiences water deficiency, its leaves may turn yellow or brown from the tips inward.[3] This northern red oak (Quercus rubra) shows signs of drought and leaf scorch. Note how the brown areas start at the tips of the leaves, and the internal sections of the leaf are yellowing.
If a dry period persists, some trees may exhibit early fall color and/or early leaf drop.[4]
Photo: South Dakota State University Extension
Photo: Alabama A&M and Auburn Extension
Stunted Growth or Dead Branches: Drought can lead to reduced growth, including shorter stems, smaller leaves, thinner foliage, and fewer flowers or fruits. It can also cause dead branches and defoliation at branch extremities.
Photo: Alabama A&M and Auburn Extension
Photo: University of Maryland Extension
Understanding Drought’s Impact
We all know that trees and plants need water, but what happens when they do not get enough? As the available water in the soil decreases, the tree’s fine hair-like roots, which are primarily responsible for absorbing moisture, begin to die.[5] With prolonged drought, even larger roots die back. Once this occurs, the tree will need time to regrow the roots and root hairs needed to absorb rainfall or other water provided. This process may take days or even weeks. Trees impacted by root loss are also at greater risk of pest damage and disease.
Evaluating Recovery Potential
1. Examine Turgor Pressure: Hydrated plants and trees have turgor pressure, giving them their firm, upright structure. If a plant is able to regain this pressure after watering, it is a positive sign of recovery. This is just a fancy way of saying you should water the tree or plant to see if it bounces back!
2. Look for New Growth: Look for signs of new shoots, leaves, or buds. This indicates that the plant is directing its resources toward recovery.
3. Examine Roots: If you see no signs of growth above ground, you may want to gently dig around the base of the tree or plant to assess the condition of its roots. Healthy roots should be firm, white and pliable. If they are brown, brittle, or mushy, it may be a sign of irreversible damage.
4. Be Patient! Remember that recovery takes time, sometimes even weeks or months. Wait until next spring to make a final determination. You may be pleasantly surprised to find your beloved plant or tree has regrown roots and regained its strength during fall and winter, given these seasons often have more precipitation and temperatures conducive to root growth.
Assisting in Recovery and Drought-Stress Prevention
1. Proper Watering: Water deeply and consistently. Frequent shallow watering encourages shallow root growth, which is more susceptible to drought because it can dry out and die more easily. Ironically, overwatered plants often exhibit the same symptoms as plants damaged by drought, so avoid the temptation of flooding your garden to avoid drought or to assist recovering plants.
Image by Phichit Wongsunthi from Pixabay
- Mature Trees with Established Roots: As a rule of thumb, mature trees need about one inch of rainfall per week. Mature trees can often “ride out” temporary drought conditions because of their extensive root systems. Here are some tips to determine whether periodic droughts may require you to perform supplemental watering for mature trees.
- Identify Drought-Stressed Trees: Using the factors listed at the outset of this article (wilting, leaf browning/yellowing, leaf scorch or drop), look for trees under stress. Large, mature trees with undisturbed root systems should only be watered if signs of drought are observed. You might also check resources like those at the Virginia Department of Environmental Quality, to identify the extent of drought throughout the state.
- Check Soil: Dig a hole 6-9 inches deep. If soil is moist and cool, no need to water.
- Watering Range: A mature tree’s roots spread like a pancake under the tree, often extending two to three times the area of the dripline. For that reason, water the entire area under the tree’s dripline and beyond and avoid watering the trunk and foliage, where excess moisture may promote disease.
- Water Quantity and Timing: Start by applying one inch of water per week. If using a sprinkler, place containers in relevant areas and measure how long it took for them to acquire an inch of water to give you an ideal watering timing for the future. To test if water is penetrating, dig a hole six inches deep to see if soil is moist; if not, add another half an inch of water. Best practice is to water in early morning to avoid evaporation of the irrigation by sun and heat.
- Consider Context: Based on soil type (sandy, loamy, or clay) or tree location (on a slope), you may need more or less water to achieve the desired result.[6]
- New Trees: You should water new trees a minimum of two times a week during the establishment period. For more growth, water trees daily for the first month, and continue with two or three times per week for the remainder of the establishment period. Water trees slowly to prevent runoff and ensure a deep soaking. There are several slow-release watering sacks that can make watering less burdensome. Spring and fall are the best times to plant because they are cooler and wetter than summer.
- Trees and Plants in Containers: Containers will dry out faster than soil in the ground, so be sure to provide enough water for this environment. How quickly your container will dry out will depend on its material (plastic vs. terra cotta), where the container is located (sun or shade), and the size of the container. Evaluate water needs by digging two inches down and feeling whether the soil is cool and moist. Permeable containers on a hot stone patio may require daily or even twice-daily watering during peak summer days.
- Watering Systems: Beyond slow-release watering sacks, you might also investigate water-wise drip systems or soaker hoses on a timer that can allow you to adjust watering frequency based on current weather conditions. Irrigation systems, while costlier, can provide the convenience of adjusting watering remotely on your phone or computer, which is helpful if you are away.[7]
2. Mulching: Applying a layer of organic mulch around the base of the tree or plant helps retain soil moisture, regulate soil temperature, and prevent weed competition. Make sure to leave an inch or two between the mulch and trunk.
3. Pruning Out Dead Branches: Remove any dead or severely damaged branches to redirect the plant’s energy toward healthy growth. Eliminating dead branches will also help limit pests that are drawn to dead wood.
4. Adding Compost: Compost is rich in nutrition, and promotes soil health and root growth by holding more moisture.
5. Planting Drought Resistant Trees and Plants: Some plants and trees handle drought stress better than others. Check out our website for suggestions here. Generally, drought tolerant trees have thicker and waxier leaves that minimize water loss through their foliage. All trees transpire moisture through leaf opening called stomata, needed for photosynthesis and growth. Some drought tolerant species include:[8]
- Oaks
- Sassafras
- Hickories
- Persimmon
- Gingko
- Hollies
- Hackberry
- Eastern Redcedar
- Black and Honey Locust
- Longleaf Pine
- Elms
6. Looking to the Future: MIT is developing electronic sensors that could be placed on leaves to indicate drought conditions. Though still under development, this is a sign that maintaining plant health during drought has caught the attention of creative scientists.[9]
Conclusion:
Though drought stress can be a significant challenge for trees and plants, timely intervention and proper care can greatly improve their chances of recovery. By recognizing the signs of drought stress in plants on your property, evaluating their potential recovery, and implementing effective strategies, you can help your green companions thrive once more (and reduce the guilt of forgetting to water when life gets in the way.
References:
[1] See Virginia Department of Environmental Quality, at https://www.deq.virginia.gov/our-programs/water/water-quantity/drought.
[2] See US Drought Monitor, at https://droughtmonitor.unl.edu/CurrentMap/StateDroughtMonitor.aspx?VA.
[3] Trees & Drought Stress, Professor John Ball, University of South Dakota Extension, https://extension.sdstate.edu/trees-drought-stress
[4] University of Maryland Extension, at https://extension.umd.edu/resource/drought-and-excessive-heat-stress.
[5] Drought and Landscape Trees: Effects, Signs, and Watering Guidelines, by Beau Brodbeck and Jack Rowe, Alabama A&M and Auburn Extension, November 3, 2022, at https://www.aces.edu/blog/topics/landscaping/drought-and-landscape-trees-effects-signs-and-watering-guidelines/. Hereinafter Alabama A&M and Auburn Extension.
[6] Alabama A&M and Auburn Extension.
[7] Drought and Water Stress, Missouri Botanical Garden, https://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/environmental/drought.
[8] Alabama A&M and Auburn Extension.
[9] Sensors applied to plant leaves warn of water shortage, Anne Trafton, Nov. 8, 2017, MIT News, at https://news.mit.edu/2017/sensors-applied-plant-leaves-warn-water-shortage-1108.