Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
1/7/03
Contacts:
Richard Jauron, Horticulture, (515) 294-1871, rjauron@iastate.edu
Diane Nelson, Continuing Education and Communication Services, (515) 294-3178,
dinelson@iastate.edu
Dry Winter Weather Effects on Landscape Plants
AMES, Iowa -- Many parts of Iowa have received little or no precipitation over the past two months. The dry weather has raised concerns about the condition of trees, shrubs and perennials.
"Despite the recent dry weather, most healthy, well-established trees and shrubs are probably fine at this time," said Richard Jauron, Iowa State University Extension horticulturist. "Most areas in Iowa received normal or above normal amounts of precipitation in October which gave plants a good opportunity to absorb water before winter."
Well-established trees and shrubs also have large, extensive root systems that allow plants to absorb moisture even when soils are fairly dry. Because deciduous trees and shrubs lose their leaves in the fall, they lose relatively small amounts of moisture during the winter.
The dry weather poses the biggest threat to trees and shrubs planted in the past one or two years. "Because of their relatively small root systems, these plants may have difficulty absorbing adequate amounts of moisture during dry weather," said Jauron. "Recently planted evergreens are especially vulnerable since they retain foliage (needles) during winter. These needles lose considerable amounts of moisture on mild, sunny, winter days."
If the soil is not frozen, Jauron says it probably would be beneficial to water trees and shrubs planted in the last one or two 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. Water should be applied slowly and directly to the root-ball or root-mass. A thorough soaking once every seven to 10 days should be sufficient. Watering is of no benefit if the ground 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," said Jauron. "If March and April precipitation amounts are well below normal, then it will be advisable to continue to water trees and shrubs planted within the past one or two years. Some well-established plants also may require watering in late winter/early spring if the dry weather persists."
Winter watering is also beneficial to perennials that were planted within the last year, and especially 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 should not be necessary to water well-established perennials.
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