Diagnose and Prevent Drought Stress in Plants

A droopy, wilting plant. It’s a gardener’s instinct to automatically assume: It needs water. And sometimes, that’s a good instinct. But low-water plants just as easily can be killed by kindness as by neglect.

gladiola
Gladiolas like an inch of water a week, but not too much water.

For example, several problems with tomato fruits are caused by too much water, or especially irregular watering. Plants, like people, need some regular hydration. You wouldn’t avoid drinking water for five days and then gulp down a liter, right? One reason drip systems are effective is the consistency (assuming you set a timer) of the amount of water they deliver, along with the slow rate of flow and the fact that they water the soil/roots and not a plant’s leaves. The delivery and slow flow help retain more moisture and nutrients around the roots.

A drip system with adjustable emitters is a great way to water our okra. And it looks like to attract ants...
A drip system with adjustable emitters is a great way to water our okra.

What’s the prognosis?

There are reasons other than drought stress that cause plants to wilt, including problems with the roots. That’s why plants you’ve just transplanted from seed or a nursery container tend to wilt for a few days or weeks. The roots suffer some damage when taken from a pot and replanted. Understand that this is part of the natural course of the plant’s life and help it through without stressing too much (meaning you, not the plant). Even though a plant is waterwise, it still needs extra water until the roots heal and begin to grow, more efficiently pulling water into the plant. If the ground is dry at root level, the roots can’t do their work. Plants that are overwatered sometimes wilt, too, further complicating the “diagnosis.”

tomato branch broke water
After our first heavy rain, I accidentally brushed against a branch of this currant tomato.It peeled off; the brown leaves are likely from that damage, not from lack of water!

Speaking of, most gardeners jump to the worst possible scenario when determining a plant problem. Although disease is a possibility, look not only for symptoms of a particular wilt or fungal disease, but also for possible causes. Do you have evidence of bugs that might have damaged leaves or carried a disease to your plant? Is the plant getting enough air circulation? Is water running off and away from the plant? Has it just been super hot for several days?

incipient wilt
Incipient wilt on a squash. Still not the best scenario and a signal to check our soil, but it’s temporary.

The best way to distinguish drought stress from other causes of wilt is by looking at and feeling the soil. Damp soil means the plant has water available; adding water at this point likely won’t help. You should feel an inch or two below the surface. One way is to stick your finger in the dirt to about the first knuckle joint.

Prevent plant stress

When a plant needs water, it’s more susceptible to damage from bugs and diseases. Pests attack the weak. You can prevent plant stress from underwatering by:

  • Checking the soil as mentioned above; see if there is water for the plant.
  • Looking for signs of underwatering. These usually include leaves turning yellow and brown, and even falling off. Typically, drought stress begins with lower leaves.
  • Thinking about the plant’s environment and how it might have changed. Is it windy and hot or muggy and cool in the evenings? Did you last water a plant in the afternoon out of necessity instead of your usual morning routine?
hot day on plant
Not much you can do about these weather conditions within a week or so of placing new plants in your landscape. Water consistently in the morning and shade plants if practical.
  • Using a meter or records when in doubt. We have an inexpensive moisture meter for our farm area. If nothing else, it helps confirm or deny my suspicions about the need to water and gives me a basis for comparing soils or drip rates around certain plants. Keeping records of watering, fertilizing and other activities can help manage and diagnose plant problems.
water meter to check moisture
Geraniums like to dry a little between watering. An inexpensive meter might not be the most accurate tool, but can help a home gardener check soil moisture.
  • It’s always better to water before a plant wilts, and not to wait until wilting occurs. Although plant roots need to seek water, they also have to find it! When no water is available in the soil around them, plants can begin reacting with wilt, slowed growth or flower and fruit production, and other signs.
xeric bush spirea
Blue mist spirea is a low-water plant. If the leaves have spots, it’s more likely getting too much water than not enough.
  • Finally, remember there is no hard and fast rule on watering. Much of the advice I see comes from areas that are more humid, cooler, less windy, and at lower altitude than our conditions here in New Mexico. Having said that, you can create conditions that help plants retain moisture, mostly by ensuring healthy soil and mulching. Containers need a little more frequent watering because they dry out faster than the ground. Water container and landscape plants slowly so the moisture drips instead of flooding down. You probably only need to add water to a container when the top few inches of soil are dry.