What is Drought Stress?
Drought stress is not a disease caused by a fungus, bacterium, or virus. It's a physiological disorder, which is a plant's negative response to a lack of available water. Essentially, it's the plant equivalent of dehydration. This happens when the amount of water a plant loses through its leaves (a process called transpiration) is greater than the amount of water its roots can absorb from the soil.
The cause is purely environmental. While a simple lack of rain is the most obvious reason, other factors can create or worsen drought stress:
- Environmental Conditions: High temperatures, low humidity, and strong, drying winds all increase the rate of water loss from leaves.
- Poor Soil: Sandy soil drains too quickly, while heavily compacted clay soil can be difficult for water to penetrate, leading to runoff instead of absorption.
- Root Issues: A small or damaged root system (common in newly transplanted trees and shrubs) can't absorb water effectively. Plants in containers are also highly susceptible as their soil volume is limited and dries out fast.
While all plants can suffer from drought, some are more vulnerable, including newly planted perennials, trees, and shrubs; container plants; shallow-rooted plants like hydrangeas and impatiens; and cool-season lawn grasses.
How Drought Stress Develops
Drought stress isn't a condition that "spreads" but rather a progressive state that worsens over time if water isn't available. The process begins inside the plant. To cool itself and perform photosynthesis, a plant opens tiny pores on its leaves, called stomata, releasing water vapor. As soil moisture dwindles, the roots can't keep up with the demand. The plant's internal water pressure, known as turgor pressure, begins to drop. This is what causes the initial wilting.
The plant will try to protect itself by closing its stomata to conserve water. However, this also shuts down photosynthesis, halting the plant's growth. If the dry conditions persist, cells in the leaves begin to die, starting at the edges where water is hardest to deliver. The damage is cumulative; a plant repeatedly stressed by drought becomes weak and is much more susceptible to attack from actual diseases and insect pests.
Symptoms
Learning to recognize the early warning signs of drought stress can help you intervene before permanent damage occurs.
Early Stage
- Temporary Wilting: The most classic sign. Leaves and stems droop during the hottest part of the day but seem to recover in the evening or overnight when temperatures cool.
- Color Change: Leaves may take on a grayish or bluish cast. In lawns, you may notice that footprints remain in the grass long after you've walked on it.
- Leaf Curling: The blades of leaves may roll or curl inward, a defensive measure to reduce the leaf surface area exposed to the sun and wind.
Middle Stage
- Permanent Wilting: The plant wilts and does not recover overnight, even when temperatures are cooler.
- Leaf Scorch: The edges and tips of leaves begin to turn yellow, then a crispy brown. This damage is irreversible.
- Stunted Growth: The plant's growth slows or stops. New leaves will be smaller than normal, and the plant may prematurely drop flowers or developing fruit to conserve resources.
Late Stage
- Leaf Drop: Scorched, dead leaves become brittle and fall from the plant, sometimes leading to significant defoliation.
- Branch Dieback: In shrubs and trees, twigs and entire branches may die, starting from the tips and progressing inward.
- Plant Death: If water is not provided, the plant's vascular system fails, and it cannot recover.
How to Control Disease Progression
When you spot the signs of drought stress, quick action is needed to help your plants. The good news is that the solution is straightforward: provide water effectively.
- Water Immediately and Deeply: The most important action is to water the plant thoroughly. A light sprinkle won't do; the water needs to soak deep into the root zone.
- Water the Soil, Not the Leaves: Apply water directly to the base of the plant. Wetting the leaves does little to help the plant and can encourage fungal diseases. Use a soaker hose, drip irrigation, or a hose on a slow trickle.
- Apply Mulch: After watering, apply a 2-3 inch layer of organic mulch (like shredded bark, compost, or straw) around the base of the plant, keeping it an inch away from the stem or trunk. Mulch is a superhero: it cools the soil, conserves moisture, and prevents weeds.
- Provide Temporary Shade: For smaller, stressed plants like perennials or new shrubs, providing temporary shade with a patio umbrella or a piece of shade cloth during the hottest part of the day can reduce water loss.
- Hold the Fertilizer: Do not fertilize a drought-stressed plant. Fertilizer promotes new growth, which demands even more water and puts additional stress on the already struggling plant.
Treatment Options
The only "treatment" for drought is water. There are no organic or chemical sprays that can solve a lack of moisture. The focus is on rehydrating the plant and its environment for recovery.
Step-by-Step Treatment Procedure
- Check the Soil: Before watering, stick your finger a few inches into the soil near the plant's base. If it's dry, it's time to water.
- Water Slowly and Deeply: Apply water slowly enough that it soaks in rather than runs off. For a small shrub or perennial, this might mean leaving a hose on a slow trickle for 20-30 minutes. The goal is to moisten the soil to a depth of 6-12 inches.
- Water in the Morning: The best time to water is early in the morning. This minimizes water loss to evaporation and allows the plant to hydrate before the heat of the day.
- Repeat as Necessary: Don't let the soil dry out completely again. Check the soil every few days during hot, dry weather and water deeply whenever the top few inches become dry.
Expected Timeline for Recovery
For a plant that is only wilting, you can see a dramatic recovery within a few hours of a deep watering. Leaves that have turned brown and crispy are dead and will not recover. However, with consistent moisture, the plant should begin to produce new, healthy growth within a few weeks.
Prevention Strategies
The best way to manage drought stress is to create a water-wise garden that is naturally resilient to dry spells.
- Choose the Right Plant for the Right Place: Select plants that are well-suited to your climate and the specific conditions of your yard. Use drought-tolerant species like coneflower, sedum, lavender, and ornamental grasses in your sunniest, driest spots.
- Improve Your Soil: The foundation of a drought-resistant garden is healthy soil. Before planting, amend your soil with several inches of compost. Organic matter helps sandy soil hold more water and helps clay soil absorb water more effectively.
- Mulch Everything: A constant 2-3 inch layer of organic mulch is one of the most effective water-conservation tools you can use in the garden.
- Water Smart: Water your established plants deeply and infrequently. This encourages them to grow deep, strong root systems that can find water far below the surface, making them much more resilient than shallow-rooted plants.
- Control Weeds: Weeds are aggressive competitors for water. Keep your garden beds well-weeded so your desired plants don't have to fight for moisture.
- Group Plants by Water Needs: Place plants with high water needs together and drought-tolerant plants together. This allows you to water more efficiently, giving thirsty plants the moisture they need without overwatering those that prefer to be dry.
