The Homeowners Column

The Homeowners Column

How Will The Cold Affect Our Plants?

Photo of Sandra Mason

Sandra Mason
Extension Educator, Horticulture
slmason@illinois.edu

We have lamented for months about our bulbs sprouting and spring flowering trees blooming in fall and winter. Plants don't have calendars but respond to the length of daylight, hours of chilling and warm weather following chilling. Temperate plants need a certain number of hours of chilling to occur in order for them to break dormancy. The number of hours needed at a certain temperature varies with the plant species. These chilling hours are accumulated, not in the coldest days of winter, but in the days when temperatures range between 32 and 45°F. Forsythia needs relatively few hours of chilling which explains why we had forsythia blooming in December or January. These shrubs will most likely not bloom or have few blooms in the spring.

At this point many of the plants have had enough chilling to break dormancy and sprout. Spring bulbs have sprouted leaves and many perennials are showing new growth. Luckily for most of the bulbs the flower is still deep inside the bulb and is quite protected. Most perennials can easily produce more leaves. A light covering of shredded leaves or snow will help to protect the plants and keep the soil temperatures down to reduce further growth. However once the flower buds show color they are much more susceptible to cold injury. So it remains to be seen what February and March will bring us in weather. I haven't figured out a way to stuff them back into the ground so we are left to wonder what the future will hold.

Our trees and shrubs are at most risk and they are harder to protect against cold. For many of the trees and shrubs the chilling requirement has been met and the warmer weather has prompted the leaves and flowers to begin to emerge from the buds earlier than normal. Once these buds begin to open, they are more vulnerable to the cold. A frost or freeze could be quite damaging to young leaves and flowers.

Tree fruit crops such as peach and apricot and early spring blooming trees such as magnolia which often have problems with late spring frosts may be in trouble this year when it comes to a good flower show. Unfortunately there is still plenty of time for us to have severe cold periods. A loss of flowers is generally not life threatening for a plant. However if a cold snap kills the leaf buds, some trees and shrubs may not be healthy enough to releaf.

It's hard to predict what will happen in your backyard. If our weather stays somewhat constant and moderate, we may have relatively few problems. How well an individual plant will survive depends on additional factors such as the overall health of the plant, plant maturity and what stage of growth it is in when cold hits. Healthy plants will survive cold temperature better than plants entering winter in poor health. Plants may make it through winter only to be killed or damaged by wildly fluctuating spring conditions. Generally more mature plants survive cold stress better than newly established plants.

We may not be able to do much but hope for good weather. As the saying goes "In this ball game, Mother Nature bats last."

A Garden Center Employee workshop will be held on February 18 from 1-4 pm. Focus will be disease identification, basic plant care, problem solving and pesticide safety. Anyone who has to answer gardening questions in their place of employment will appreciate this workshop.

Junior Master Gardener workshop for teachers and leaders February 20 from 9 am – 2:30 pm. Discover this program about teaching gardening to youth. Call U of I Extension 217-333-7672 to register for these programs held at the U of I Extension office in Champaign.

View Article Archive >>