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Winter care of potted perennials

November 24, 2010

By Debra Levey Larson
Media/Communications Specialist, University of Illinois College of Agricultural, Consumer and Environmental Sciences

URBANA, Ill.—Taking care of your potted perennial plants over the winter will ensure they are around next season to provide another year of enjoyment, said Greg Stack, a University of Illinois Extension horticulture educator.

“Container gardening is a form of gardening everyone can enjoy no matter how large or small their garden may be,” said Stack. “Those with only a balcony or patio can enjoy the pleasures of gardening just as those with areas of space. Containers can become quite elaborate, and the types of plant material can be quite varied.

“When it comes to what gardeners are putting into containers, the trend is leaning toward just about anything,” Stack added.

At one time, annuals were the majority, if not the only type, of plant material being used in containers. Now, everything from perennials to small trees and shrubs are commonly being used. And while these perennials can be treated like annuals and replaced the next season, many gardeners can’t bear the thought of having something die that has the potential of coming back. Because of this, gardeners now have to consider the best way to overwinter these pots so they can have these plants survive the winter and come back next spring.

“Perennials in pots need protection because their root system is basically above ground in a container,” he explained. “This poses problems because the root system is now subject to extreme cold injury.

“If these same perennials were planted in the ground, the roots would have the benefit of the soil to help insulate and protect the roots from potential cold injury that can kill roots, leading to a good number of the plants not coming back in the spring,” Stack added. “Above ground, that protective root insulation disappears, making the roots vulnerable to extreme winter temperatures.”

So, what can a gardener do to protect that investment in perennial plant material? There are several ways to provide needed protection.

“With any container that you are considering to use, make sure the plant material in the container is dormant,” said Stack. “Wait for temperatures to drop to the 20s for several nights, and make sure the soil in the container is moist. Plants in moist soil tend to overwinter better than those where the soil is dry. Now, you can bed them down for the winter.”

If the pots are small, and if you have garden space, dig a hole in the garden large enough to accommodate the pot up to the rim. Place the pot in the hole and backfill the hole with soil. Cover the pot with a thick layer of mulch such as straw or hardwood leaves.

If you don’t want to dig holes, gather up your pots and group them together on an inside corner of a building, preferably on the east or north side. Once grouped, mulch them with straw or hardwood leaves.

“The last way to help protect your containers is to move them into an unheated building such as a garage or shed where temperatures are slightly above freezing all winter,” he said. “This inside storage will protect them. When using inside storage, make sure to check on the pots occasionally as they may dry out. If so, apply just a little bit of water to moisten the soil slightly.

“Whichever method you choose,” Stack said, “leave the plants protected until spring weather conditions moderate and they can be safely moved back into the garden.”

From the Nov. 24-30, 2010 issue

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