Our Dry Fall Weather and the Effects on Landscape Plants

Many parts of Iowa have received little precipitation over the past 6 to 8 weeks. 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. 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. 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 not be able to absorb adequate amounts of moisture before winter. Recently planted evergreens are especially vulnerable as they retain much of their foliage (needles) during winter. These needles lose considerable amounts of moisture on mild, sunny, winter days. Because of the dry conditions, it would be wise to water trees and shrubs planted in the last 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 thoroughly soaking about once every 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.) Perennials planted within the past year would also likely benefit from watering. Also, water spring-flowering bulbs (tulips, daffodils, crocuses, etc.) planted this fall. Spring-flowering bulbs need moisture to develop a good root system before the onset of winter. A good soaking once every 10 days should be sufficient if the dry weather persists. It shouldn’t be necessary to water most well established perennials.

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