Garden News: Excessive water hurtful to landscape plants

As we reach the middle of summer, we need to keep in mind the importance of irrigating our landscape plants. It’s important to water when it’s needed, but in many cases, we often use too much water rather than too little.

Of the tremendous amounts of water applied to our landscapes, much is never absorbed and used by the plants, says LSU AgCenter horticulturist Allen Owings.

Some water is lost to runoff by being applied too rapidly; some evaporates from exposed, unmulched soil.

“But the greatest waste of water is applying too much too often,” Owings says. “By simply using effective and efficient watering methods, you can cut irrigation requirements by 10 to 30 percent and increase landscape beauty and quality dramatically while at the same time saving water.”

Lack of water can cause a plant to wilt, dry up and die. Excessive water can cause root rot; the plant wilts because it is oxygen-starved and unable to absorb moisture.

As a rule, plants can withstand moderate drought more easily than too much moisture. For this reason, Owings says, it’s important to water thoroughly yet allow the soil to become fairly dry between waterings.

Allowing the soil to dry out somewhat between waterings encourages root development at greater depths where soil moisture is highest. Plants watered frequently but lightly are more apt to develop roots close to the surface, making them more vulnerable to wilting.

Wilting happens when plants’ roots are unable to supply sufficient moisture to the stems and leaves. Sometimes a plant will wilt on a hot day because moisture is evaporating from the leaves faster than the roots can supply it.

If the soil has ample moisture, the plant will absorb water in the evening to firm up the stems and leaves. When the leaves remain wilted the next morning, however, it’s time to water, Owings says.

Environmental conditions are the primary factor affecting plant watering needs. The best time to water is in the morning or evening when air temperatures are lower than they are at midday. In the evening, however, wet foliage can encourage fungus or mildew, making plants unsightly and jeopardizing their health.

Be prepared to control diseases if you irrigate at night.

Got a gardening question? Write to GardenNews@agcenter.lsu.edu.