What You Need to Know About Watering Plants
A simple question deserves a simple answer: When is the best time to water plants?
Before they need it.
If your plants are sagging and drooping, they’re already thirsty. True, other things can cause that, including insects, diseases, really hot temperatures and, believe it or not, overwatering. But more often than not, it’s a response to lack of moisture.
What Time of Day is Best?
All things considered, it’s better to water plants in the morning than evening. First, it fortifies them for the day ahead. Second, if you’re watering from overhead, the moisture can evaporate from foliage; otherwise it remains there overnight and could cause foliar diseases. It’s almost always better to water at the base of plants with drip irrigation or a soaker hose, because it directs water to the roots and limits evaporation. (Exception: Dusty plants can benefit from an occasional overhead shower.)
Morning watering is also beneficial for annuals and vegetables, which generally have shallower roots and less access to deeper soil moisture. Some annuals are especially sensitive to lack of water, especially New Guinea impatiens. Some gardeners even plant New Guinea impatiens as a sentinel. When they’re drooping, they know to bring out the hose and water companion plants before they’re stressed.
Time of day does not matter as much with trees and shrubs as it does with flowers. With all plants, however, afternoon is the least efficient time to water based on rates of evaporation. But when a plant is struggling from lack of moisture, water it immediately. Don’t wait for “a better time.”
What About Plants in Containers?
If you’re growing container plants, in the hottest parts of the summer there’s a good chance you’ll need to water twice a day, morning and evening. The morning watering fortifies the plants for the heat of the day, and evening watering replaces what was lost. Exceptions: Succulents and cacti need less-frequent watering.
Perennials, shrubs and trees have deeper roots than annuals and can withstand water scarcity better in the short term. However, they can still succumb to drought, so don’t ignore them.
Newly installed plants require more watering until they’re established. The main thing is to conserve soil moisture with a mulch and to water slowly and deeply to encourage roots to migrate downward rather than concentrating near the top. Check soil moisture with a trowel. If the top two inches of soil are dry, you need to water whether or not plants are showing moisture stress.
One final note: Hand watering is fine for containers, but may not be adequate for plants in the ground. The reason is simple: We tend not to water individual plants long enough by hand. Better to let the hose dribble for several minutes around each plant while you scout for weeds, etc.
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