The cold, snowy winter has been difficult for plants, wildlife, and humans. Damage to landscape plants has been observed across the state.
The extended period of snowcover across the northeastern portion of the state has posed serious problems for wildlife in the area. Denied access to food on the ground, rabbits and deer have been browsing on trees and shrubs in windbreaks, home orchards, and landscape plantings.
Rabbits have been gnawing on the trunks of young, thin-barked, unprotected trees over the winter months. Damage is most extensive on crabapples, apples, pears, plums, cherries, serviceberries, poplars, and willows. On some trees, the bark has been removed completely around the trunk, effectively girdling them. Rabbits have also fed on deciduous shrubs. Damage has been observed on winged euonymus (burning bush), dogwoods, cotoneasters, viburnums, roses, and spireas. Rabbits have girdled large stems and snipped off small twigs.
Trees that have been completely girdled have essentially been destroyed. Wrapping the trunk or applying pruning paint to the damaged area will not save the tree. Most affected trees will sucker from the base. However, since most fruit and ornamental trees are propagated by grafting, suckers which originate from the rootstock will not produce a desirable tree.
Most deciduous shrubs have the ability to produce new shoots or suckers at their base. Because of this ability, most severely damaged deciduous shrubs will eventually recover. (It may take some shrubs several years to fully recover.) Girdled stems should be cut off just below the feeding injury.
Deer have also damaged trees and shrubs in the state. Deer have browsed on arborvitae, yews, pines, and other evergreens over the winter months. On some evergreens, all green growth has been eaten off as high as the animals could reach.
The key to the condition of deer-damaged evergreens is the presence of growing points or buds on the browsed branches. Branches that have had all their buds devoured by deer will not produce new growth in spring. As a result, some small evergreens may have been destroyed. Larger evergreens may have permanently lost their lower branches. Since buds on arborvitae and yews are rather difficult to see, individuals should wait until late spring before taking any action. Branches that are completely bare (no green growth present) in early June have been destroyed and can be removed.
Cold Temperature Damage
This winter's cold temperatures may have damaged peach and sweet cherry trees. Peach trees are not reliably cold hardy in much of Iowa. Temperatures below -18 degrees Fahrenheit will destroy the flower buds on peach trees. Temperatures of -25 degrees or below may damage or destroy the peach trees themselves. The flower buds on sweet cherries are slightly more cold hardy than those on peaches. The flower buds on some sweet cherry cultivars can survive temperatures down to -20 degrees Fahrenheit. Iowa gardeners should expect poor crops on peaches and sweet cherries this summer. It is also possible that the trees themselves may have been damaged. Damage may vary from dieback of twigs and branches to complete death. On a brighter note, the cold winter temperatures should not have damaged most apple, pear, and sour (tart) cherry trees.
Ornamental trees and shrubs that are native to Iowa (or similar regions of the world) are well adapted to our climate and should have suffered little or no damage. However, marginally hardy plants, such as Japanese maple (Acer palmatum), flowering dogwood (Cornus florida), and Japanese flowering cherry (Prunus serrulata) may have sustained damage. (The maximum cold hardiness of most Japanese maple, flowering dogwood, and Japanese flowering cherry cultivars is -20 degrees Fahrenheit.) Damage may vary from the dieback of twigs and branches to complete death of the tree.
This winter's cold temperatures may have also destroyed the flower buds on flowering quince (Chaenomeles spp.) and some forsythia cultivars. Temperatures of -20 degrees Fahrenheit or below likely destroyed the flower buds on flowering quince and 'Lynwood Gold' and 'Spring Glory' (two popular forsythia cultivars). As a result, these shrubs will likely produce few, if any, flowers in spring. Fortunately, the cold temperatures should not have any long term effects on the shrubs. The leaf buds on flowering quince and forsythia are hardier than their flower buds. The shrubs should leaf out normally in spring.
This winter's cold temperatures should have little impact on the flowering of most shrubs. Lilacs, viburnums, dogwoods, and spireas possess excellent cold hardiness and should bloom normally this spring. Forsythia cultivars 'Meadowlark' and 'Northern Sun' should also bloom well as their flower buds can tolerate temperatures to -30 degrees Fahrenheit.
The needles on some evergreens have begun to turn brown in recent weeks. Browning of yews, arborvitae, boxwoods, pines, and spruces in late winter or early spring is usually due to desiccation injury. Evergreen foliage continues to lose moisture during the winter months, particularly on windy or sunny days. However, once the soil freezes, the plant's roots are no longer able to absorb moisture. Foliage exposed to the drying effects of the sun and wind may eventually dry out and die. (Last summer's dry weather may have made the evergreens more susceptible to desiccation injury.) While desiccation injury occurs during the winter months, the browning of the needles often doesn't occur until late winter or early spring. Damage is most often located on the south and west sides of evergreens.
The brown needles on affected trees and shrubs have been destroyed and will eventually fall off. However, the vegetative buds on the damaged evergreens may still be alive. Live buds will break in spring and produce new growth. Evergreens that have sustained light to moderate damage may look much better by late spring. A light application of fertilizer in early spring and watering during dry weather will encourage new growth and speed recovery of damaged plants. Areas that are completely brown in early June are dead and should be pruned out.