How and When to Water Your Perennials

By The National Gardening Association, Bob Beckstrom, Karan Davis Cutler, Kathleen Fisher, Phillip Giroux, Judy Glattstein, Mike MacCaskey, Bill Marken, Charlie Nardozzi, Sally Roth, Marcia Tatroe, Lance Walheim, and Ann Whitman from Gardening All-in-One For Dummies

Most perennials require water only after the top few inches of soil dry out, but before the plant starts to show symptoms of drought stress. Perennials from arid habitats benefit when the dry interval between waterings is longer. Plants from wet places prefer to never completely dry out. Problems occur when the soil is either too wet or too dry for too long. To complicate matters, overwatered and underwatered perennials exhibit nearly identical symptoms. Both conditions cause plants to wilt and droop miserably, to develop yellowed leaves with brown edges, and to experience stunted growth. Flowers and leaves start to drop off, and eventually, the plant dies.

You need to feel the soil to be certain whether the soil is too wet or too dry. When your perennials first start to show signs of stress, dig a small hole several inches deep and feel the soil. If the soil’s wet, you know that you need to cut back on water. If the soil is dry, water more frequently. Clay is more difficult to judge than sand. The tiny clay particles can grab hold of moisture so tightly that the soil can feel cool and somewhat moist, and yet the plants can’t get the water. Amending clay soil with plenty of organic matter alleviates this problem.

Don’t water in the hottest part of the day. Much of the water from a midday watering evaporates before it has a chance to soak in. The same goes for watering when a wind is blowing. Watering in the evening or early morning is preferable wherever you live, but keep in mind the following tips:

Water whenever the soil is dry and plants are wilting or showing signs of imminent death. Most perennials wilt on a hot day, regardless of whether or not they need water. Water only when the soil is dry and the plants don’t recover from their “faint” overnight.
Choose morning watering over evening watering. Mornings aren’t as windy as evenings, so less water gets blown away. Also, the moisture from a morning watering recharges your plants for the day. In tropical regions, wet foliage may help spread some diseases. If you live in a steamy, damp climate, it’s especially important to water early in the morning, so that leaves dry off quickly as the day heats up.
Water in the evening if you live in a dry region. That way, plants have ample time to absorb the water overnight.

Newly transplanted perennials are especially vulnerable in the first few weeks. Extra pampering gets them off to a good, strong start. Little root balls can dry out very quickly. During really hot spells, you may need to water more than once a day. Water new transplants every time their roots dry out, whether the surrounding soil is still damp or not. The only way you can tell whether the root ball is dry is to push your fingers into the soil at the base of each plant and feel for yourself.

A process called wicking can cause a newly planted root ball to remain absolutely dry, even while standing in a puddle of mud. Wicking can occur whenever two different types of soil meet. The soil in the prepared flower bed is almost always heavier and denser than the potting mix surrounding the root ball. Moisture is pulled out of the light soil, leaving the new plant high and dry. After a few weeks, the roots travel out into the new soil, and the problem is solved. But in the meantime, you must make certain that the root ball is actually getting wet.