The prolonged warm weather has some growers and gardeners worried. Wisconsin has experienced warmer than usual winter temperatures this year, but fluctuations can occur between years or during a single season with the return of normal, colder temperatures say University of Wisconsin-Extension horticulture experts.
With continued warm weather, flowering bulbs such as daffodils, tulips and other spring flowers have emerged sooner, up to a month earlier than usual. Red and silver maples have started to flower along with a few other plants a month before normal. If we continue to see these warmer temperatures, followed by below freezing temperatures, significant damage can occur. Flowering bulbs such as daffodils are protected somewhat if the flowers themselves have not opened, but the emerging leaves and open flowers can be damaged with temperatures below freezing. Significant bud swell on tree and shrub branches has occurred already. The dormancy requirements of plants have been completed and now the buds are ready to begin opening with rising air and soil temperatures and increased day length.
Is there anything we can do about it? Laura Jull, UW-Extension woody ornamental specialist said, “There is not much we can do about it since Mother Nature cannot be controlled, however, a good bark mulch on top of the soil will help moderate soil temperatures compared to bare soil. Covering emerging bulbs with leaves during a severe cold snap will help protect the emerging shoots, but should be removed during warmer temperatures in order to avoid wet conditions on top of the bulbs, which can lead to rot.”
She added, “Leaves on trees and shrubs have not emerged, except for plants in areas prone to be warmer such as courtyards and south facing walls. Most of our native trees and shrubs have not leafed out yet, but with prolonged unseasonably warm temperatures, buds may break not only due to increased air temperatures, but also warming soil temperatures.”
What about fruit trees and shrubs? Patty McManus, UW-Extension fruit pathology specialist said, “Fruit tree flower buds are fairly resistant to frost until flowers start to emerge. However, if fruit trees start to bloom, and then we have a return of freezing temperatures, the flowers will be killed and fruit production reduced significantly or lost entirely. The degree of damage depends on how advanced flower buds are, how low the temperatures are, and the duration of freezing temperatures. Even if flowers are killed, apple trees will still produce leaves, and the long-term health of the tree will not be compromised.
“However, frost during bloom predisposes cherry and other stone fruit trees to various fungal and bacterial canker diseases, which in turn reduce the tree's long-term health. Unfortunately, there are no effective treatments to apply under such conditions,” McManus noted.
What about grape vines? Rebecca Harbut, UW-Extension fruit crops specialist said, “In terms of managing the risk, more buds can be left on grape vines than typical so that if we do get a frost, additional buds left on the vine might make it through the frost as all the buds on the shoots do not develop at the same time.”
Agriculture and natural resources is a program of the University of Wisconsin-Extension, Cooperative Extension in partnership with local, state and federal government in each Wisconsin county.