AMES, Iowa -- Winter can be tough on Iowa’s trees and shrubs. Low temperatures, rapid temperature changes, winter desiccation and the weight of ice and snow can damage vulnerable trees and shrubs. Horticulturists with Iowa State University Extension and Outreach answer questions about the effect this winter’s frigid temperatures will have on landscape plants. To have additional questions answered, contact Hortline at 515-294-3108 or email@example.com.
The cold temperatures may have damaged peach and sweet cherry trees. Peach trees are not reliably cold hardy in much of Iowa. Temperatures below -18 F will destroy the flower buds on peach trees. Temperatures of -25 F 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 of -20 F. Iowa gardeners should expect poor crops on peaches and sweet cherries this summer. It also is 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 apples, pears and sour (tart) cherries.
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 F.) Damage may vary from the dieback of twigs and branches to complete death of the tree.
This winter’s cold temperatures also may have destroyed the flower buds on flowering quince (Chaenomeles spp.) and some forsythia cultivars. Temperatures of -20 F 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 likely will 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 forsythia cultivars ‘Meadowlark’ and ‘Northern Sun.’ The flower buds of ‘Meadowlark and ‘Northern Sun’ can tolerate temperatures to -30 F.
This winter’s prolonged period of snow cover has deprived deer of food on the ground. As a result, deer have been feeding on trees and shrubs in woodlands, windbreaks and home landscapes. Among evergreens, arborvitae and yews are most susceptible to browsing by deer in winter.
The extent of damage to the lower portions of the arborvitae will be determined by the presence or absence of buds (growing points). If buds are present, the lower branches will produce new growth in spring. The new growth should be apparent by early summer. The lower portions of the arborvitae will remain bare and likely never develop new growth if no buds are present.