Landscape - Watering Trees and Shrubs

With the current drought in mid-state it is critical to water trees and shrubs to prevent premature defoliation

While many homeowners are diligent to keep their lawns watered and green, trees and shrubs often get ignored. Reducing stress to trees and shrubs this time of year is critical. As we go into the fall, trees are shifting internal resources and undergoing physiological changes that will enable them to withstand the rigors of the winter to come. If plants are subjected to severe stresses now, they will be more predisposed to various winter injuries. With this in mind, irrigating trees and shrubs is important in landscapes.

Give good, long soakings rather than frequent light waterings. A typical rule of thumb is to provide at least one inch of irrigation per week. How many gallons of water this translates into depends on the size of the tree. If we measure the width of crown spread of a tree we can calculate the area under the drip line. We can then figure the volume of water needed to cover this area with one inch of water.

Increase the irrigation amount as temperature soar. The one inch per week is a good rough guide but peak evaporative demand can approach three inches per week in Delaware during extremely hot summer weather.

Apply mulch properly. Mulching is the best way to conserve precious soil moisture in the landscape.

Use irrigation bags on newly established trees. Gator bags are designed to provide about 15 gallons of water over several hours, providing an easy way to ensure a slow steady watering. Gallons of water needed to provide 1 inch of irrigation under the dripline of trees of various sizes

Don’t allow water to run-off. Water that runs off is wasted water. If you’re watering by hand and notice water running off, move from tree to tree to allow water to soak in before resuming watering.

Wilting leaves, leaf scorch, dropping leaves and drooping leaders in conifers are signs of water stress. If using overhead sprinklers, some experts argue against watering late in the evening due to possible disease problems associated with wet foliage. Morning is the best time to water.

Adapted from the Michigan State University Landscape Alert Newsletter.