Author Teresa Odle
For water conservation and plant health, the smartest xeric strategy is to water the roots of the plant and avoid watering the plant’s leaves.
Let’s look at the water savings first: Water evaporates when exposed to air, and occurs at the water surface area. The smaller a drop of water, the higher the percentage of the drop’s surface area. Add the effect of wind on tiny drops of water from sprinklers and you might as well just pour that water down the drain. And if you irrigate a plant from above or with sprinklers and spray emitters, much of the water lands on the leaves, where it can evaporate. In fact, water constantly evaporates from a plant’s leaves as it is, in a process called transpiration. It’s a plant’s natural way of cooling off on hot summer days.
Water The Plant’s Roots
It’s much better for a plant to take new water in through the plant’s roots, where the water picks up soil nutrients and works its way up the trunk and stems back to the leaves to do its cooling and feeding work. There’s another reason not to spray water on plant leaves, especially late in the day or during cloudy, humid weather: wet leaves can harm many plants.
Fungal diseases such as powdery mildew on roses or apple scab on apple trees and crabapples is partly a result of water on the leaves. Sometimes, there is nothing a gardener can do. We have an old apple tree with some scab that likely came from spores in old leaves left on the ground and a week or more of cool, cloudy and humid weather in late spring.
Change How You Irrigate
Often, simply changing irrigation practices can improve a plant’s health. Bubblers or drip irrigation might require a little more planning, better leveling of the soil and more parts or emitters. But in the end, the homeowner will save money on their water bill and on replacing plants! Farmers also know this is the way to go, and many are learning new ways to improve irrigation techniques to reduce water use.
Here’s yet another reason to water with drip emitters or by hand near the roots of a plant instead of broadcast or spray irrigation: weeds. When you spray water, you water everything around, including weed seeds. Watering only around your vegetables’ or ornamentals’ roots confines weed growth, making it easier to pick small weeds out by hand.
You can’t control rain, which obviously comes from overhead. But keeping plants exposed to proper sun, trimmed and cleared to give them sun and airflow and cleaning out debris from around the bottom of trees and plants can help reduce risk of fungal diseases.