Waning Winter Chill, Weaving Weather, and Worried Plants
My, what warm weather we have been having lately. This past holiday season, I was outside in shorts, soaking up the sun. Instead of a white Christmas, the Midwest blessed us with a bright and sunny Christmas. Although humans can tolerate the large swings in temperature from week to week, the performance of our landscape plants can suffer from such variability. Consistent cold temperatures in winter will keep most plants in dormancy, but when temperatures are mild and fluctuate often, tender plant parts can become damaged.
Spring bulbs are among the most delightful aspects of the beginning of the growing season. The colorful flowers are a beautiful sight after 3 months of seeing bare trees and brown grass. But what happens if the weather is not consistently cold during the dormant period that winter provides? A couple of things can happen. First, your bulbs could push out foliage right before a hard freeze. In the Midwest, daffodils, crocuses, snowdrops, and grape hyacinths come to mind when seeing green foliage push through the snow. Even though their foliage will be subject to freezing temperatures, they typically don’t abort their flowers. In fact, I recall many years when spring bulbs bloomed during a snow event in late winter or early spring. But there are plenty of bulbs that will die back from a brutal freeze if their foliage or flower buds are exposed. Iris, peonies, surprise lilies, or any bulbs that grow or flower in late spring do not like to be exposed when temperatures drop far below freezing.
Mild winters can also play a role in determining the height of our spring flowers. When cold treatment is cut short, the development of plant hormones that regulate flower height is disrupted as well. These hormones develop during dormancy and are a metaphorical gas pedal for plant growth. The longer the dormancy, the more get-up-and-go the gas pedal has. This isn’t going to kill the bulbs, but it is a little disappointing when your tulips are blooming three inches from the soil.
What about trees and shrubs? You may not know, but trees and shrubs are actually very active internally as temperatures become warmer. Maple trees in syrup production are an example of this. When temperatures are above freezing, the sap inside the tree flows, carrying essential nutrients and plant hormones to the tips of the branches, where they further develop flower and leaf buds. When there are enough warm days in spring, those buds pop open, signaling the start of the growing season. Trees that open too early can fall victim to late freezes. Saucer magnolias, Florida dogwoods, as well as some fruit trees such as plums, apricots, and peaches, can all experience cold injury from freezing temperatures.
What can be done to prevent this damage? If you have low-growing plants, covering them during cold snaps with frost blankets, cold frames, or a row cover of some kind will protect your plants from damage to a certain extent. If it is too cold, covering will not protect tender growth. Trees and shrubs, on the other hand, can’t be easily protected in the same way. One way to protect all plants would be to mulch your flower beds and tree rings properly with a layer 2-4 inches deep. Most perennial plants can bounce back from cold injury, so making sure that the root zone is not also experiencing damaging conditions like freezing and drought will help your plant come back to life for the rest of the growing season.
by Markis HIll, Horticulture Turf and Ornamentals Agents, February 2026