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Horticulture and Home Pest News
Horticulture & Home Pest News is filled with articles on current horticulture, plant care, pest management, and common household pests written by Iowa State University Extension specialists in the Departments of Entomology, Horticulture and Plant Pathology.

Winter Effects on Garden Plants

This article was published originally on 5/18/2001

The weather experienced this past winter had damaging effects on a diverse group of garden plants. From snow mold on our lawns to the death of some of our prized trees and shrubs, it seems no one group of plants was spared. While some plants were killed outright, others faired amazingly well.

A few of the casualties and survivors from the "Winter of 2000-2001" are listed below.

Trees and Shrubs

Several marginally hardy trees and shrubs succumbed to winter's onslaught of low temperatures, snow, wind, and sun.

Browning of evergreen foliage can be seen on pines, spruces, firs, yews, and arborvitae. Damage is most evident on the south and west sides of trees and shrubs. Recent studies indicate that winter injury results from a complex interaction of minimum temperature, number of freeze/thaw cycles, cooling rate, and thawing rate. Many of the damaged pines and spruces have begun to grow and should look much better in a few weeks. However, many damaged yews exhibit little or no new growth at this time. Damage to broadleaf evergreens, such as boxwood, has also been observed.

A noteworthy characteristic of the rose-of-sharon (Hibiscus syriacus) is that it leafs out rather late in the spring (typically mid to late May in central Iowa). This year , however, it appears some of the shrubs have died. Rose-of-sharon is listed as hardy in USDA Hardiness Zones 5 to 8. Winter injury is often observed when winter temperatures drop to -20 F or below.

Dieback on weigelas (Weigela florida) is a fairly common occurrence after difficult winters. The winter of 2000-2001 was no exception. Many of the shrubs have died back to near ground level. Fortunately, most of the weigelas are sprouting at their bases and will eventually recover. Gardeners should simply prune out the dead wood.

While red maples (Acer rubrum) are common sights in Minnesota and Wisconsin, they often don't perform well in Iowa. Those red maples that have managed to do well in Iowa have suffered some twig dieback this spring. The dieback is probably not due solely to our brutal winter. Our dry weather in recent years may have been a contributing factor.

Perennials

Yucca (Yucca species) seems to have been a big loser in the battle with "Old Man Winter." Many gardeners across the state have lost entire plants. But all hope is not lost; inspect yucca plants carefully before removal. Some plants may try to regrow from their base.

Yucca was not the only casualty this winter. Pinks (Dianthus species) and lamb's ear (Stachys byzantna) were others that took a beating. Many perennials such as pinks and lamb's ear abhor wet soils during the winter months. The moisture and weight of several inches of snow for long periods probably led to death of these plants.

Garden mums (Chrysanthemum x morifolium) often winterkill in Iowa. Despite a protective covering of snow during most of the winter, large numbers of mums did not survive this past winter. Highest morality rates are usually found in wet, poorly drained soils and in windy, exposed sites.

In contrast, some other perennials over-wintered surprisingly well. Delphiniums (Delphinium species) in many locations enjoyed the insulating effects of the snow. Butterfly bush (Buddleia davidii) and Russian sage (Perovskia atriplicifolia) were among many of the perennials that did not die to the ground this year because of the blanket of snow.

The unpredictability of Iowa's winter should encourage gardeners to diversify their plantings and thereby limit the amount of damage or death sustained in a single year. These "test winters" or "learning experiences" allow us to re-evaluate the plants in our garden. Those plants that don't pass the grade provide opportunities for gardeners to select plants that can survive Iowa's harsh weather.



This article originally appeared in the May 18, 2001 issue, pp. 57-58.

Year of Publication: 
2001
Issue: 
IC-485(11) -- May 18, 2001