Rosie Lerner, Purdue Consumer Horticulture Specialist
Released 5 November, 1998
Many of us gardeners have mixed feelings about this time of year: sad to see another garden year draw to a close, but at the same time relieved to get a break from the chores of weeding, watering, pruning and more weeding. But before you hibernate, there are still a few more chores to take care of outdoors.
Winter mulch isn't necessary for all garden plants, but it can mean survival for some less hardy plants. Winter mulch has a different purpose than summer mulch. The main benefits of winter cover are to protect against wide temperature fluctuations in the soil and to prevent extreme cold temperatures from harming plants.
Soil tends to heave when subjected to wide temperature changes, pushing plant roots up out of the ground. Heaving is most harmful to relatively shallow-rooted plants, such as strawberries and newly planted specimens of any kind that have not yet had a chance to develop solid footing. Winter mulch also prevents extreme cold damage to above-ground plant parts.
In most cases, 2 to 4 inches of mulch, such as straw, pine needles, hay or bark chips, give adequate protection. For some plants, such as roses, more elaborate protection is needed.
Timing is critical when applying winter mulch. It's best to wait until after temperatures are consistently below freezing to apply the mulch. Applying too early can smother the plant and encourage disease development.
Winterizing your landscape plants is just as important as winterizing your car. Those bright, sunny days of winter may be a welcome sight to us humans, but they can spell trouble for some landscape plants. Direct sunshine on young thin-barked trees warms the bark considerably. But when the sun goes down, air temperatures drop rapidly, and that can result in the tree's bark splitting. Other types of winter injury are also common, including breakage from heavy snow and ice, severe drying and animal feeding damage. However, you can help protect your plants by properly preparing them for the winter season.
Shading young, thin-barked trees such as maples and fruit trees on the south and west sides will help prevent bark splits from temperature extremes. The bark tends to split vertically on the sunny side of the tree, because as the temperatures drop rapidly at sundown, the outer bark cools down and contracts faster than the inner bark. Thus, the outer bark must split to accommodate what's below. Wrapping the trunks with commercial tree wrap provides some protection.
You can't do very much about excessively low temperatures. But you should be sure that the plants chosen for the landscape are hardy to our average winter conditions and otherwise adapted to the individual site conditions.
All plants, but especially evergreens, are susceptible to drying out over winter. The above-ground parts, such as twigs and evergreen leaves, are very much alive and are continuously losing water through a process called transpiration. Once the ground is frozen, the plant's roots are not able to take up water to replace that which is lost through the tops. The result is drying leaves, buds and twigs. Sunny, windy conditions cause water to be lost from the tops more rapidly, further aggravating the situation. Broad-leaved evergreens are particularly susceptible since they have a greater leaf surface to lose water from.
Making sure the plants have a sufficient supply of soil moisture before the ground freezes will help create healthier specimens to fight the winter battle. Water thoroughly every seven to 10 days if fall rains are not sufficient. Shading susceptible plants from winter sun and wind also can be helpful. Burlap can be fastened to stakes, or a section of snow fencing should be adequate. Plant highly susceptible plants, such as rhododendrons, on the north side of the house or a hedge to avoid strong winter sun.
Multistemmed shrubs seem to be particularly prone to damage from heavy snow and ice loads. The intense weight of snow and ice bends branches to the ground, breaking the bark and cutting off circulation of the food manufactured by the leaves to the roots. Starving roots eventually die, which leaves the tops without a supply of water, and eventually the whole plant will die. The process could take several years.
To prevent damage from heavy loads, support multistemmed plants by bundling the stems together using burlap, canvas or chicken wire. Simply binding stems together with cord will do in a pinch. Be sure to carefully remove heavy snow as soon as possible, but don't try to remove ice. More damage to the bark probably will occur than if the ice is allowed to melt on its own.
Now you've earned that trip to the Bahamas!
Last updated: 10 April 2006
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