Dry Winter Weather and its Effects on Landscape Plants

Many parts of Iowa have received little or no precipitation over the past 2 months. The dry weather has raised concerns about the condition of trees, shrubs, and other landscape plants.

Despite the recent dry weather, most healthy, well-established trees and shrubs are probably fine at this time. Most areas in Iowa received normal or above normal amounts of precipitation in October. The October rains and snows gave plants a good opportunity to absorb water before winter. Additionally, well-established trees and shrubs have large, extensive root systems. These extensive root systems allow plants to absorb moisture even when soils are fairly dry. Finally, deciduous trees and shrubs lose their leaves in the fall. As a result, deciduous materials lose relatively small amounts of moisture during the winter.

The dry weather poses the biggest threat to trees and shrubs planted in the past 1 or 2 years. Because of their relatively small root systems, these recently planted materials may have difficulty absorbing adequate amounts of moisture during dry weather. Recently planted evergreens are especially vulnerablebecause they retain much of the foliage (needles) during winter. These needles lose considerable amounts of moisture on mild, sunny, winter days.

If the soil is not frozen, it probably would be beneficial to water trees and shrubs planted in the past 1 or 2 years. The roots of recently planted trees and shrubs are mainly confined to the plant's root-ball (balled and burlapped material) or root-mass (container grown plants) and the soil immediately around them. When watering these plants, slowly apply water to the root-ball or root-mass. A thorough soaking once every 7 to 10 days should be sufficient. Watering can be discontinued when the ground freezes. (Plant roots are unable to absorb moisture when the soil is frozen.)

If the dry conditions persist into March or April, the threat to trees and shrubs is likely to become greater. Trees and shrubs require larger amounts of moisture in late winter/early spring as they break dormancy and begin to grow. Continue to water trees and shrubs planted within the past 1 or 2 years if March and April precipitation amounts are well below normal. Some well-established plants also may require watering in late winter/early spring if dry weather persists.

Additional landscape plants that may benefit from watering are perennials planted in 2002. Watering also would be beneficial to those perennials that don't die back to the ground in fall. A good soaking once every 10 days should be sufficient if the dry weather persists. It shouldn't be necessary to water well-established perennials.

The dry weather concerns have also included home lawns. Dave Minner (ISU turfgrass specialist) recently sampled several lawns in the state. All of the samples were alive. Established lawns should be fine and do not need to be watered. Lawns most at risk are those growing on sandy soils or south-facing slopes. Late-seeded lawns (October) also may be susceptible to injury. Individuals should examine those lawns that are most at risk to injury. If the soil and the turfgrass crowns are dry, watering may help hydrate the crowns and prevent injury.

This article originally appeared in the January 17, 2003 issue, p. 2.


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