Overwintering Perennials in Containers
by Karen Weiland, Advanced Master Gardener
Growing perennials in containers is a very popular practice. Containers do not provide the roots with the protection they need during cold weather. A layer of mulch and snow can act as a blanket that protects perennials in containers during the winter months. Snow in the winter is what wood chips are in the summer….think protective mulch.
After a couple of killing frosts, make sure your pots are well watered then group your potted perennials together along an area of your house, out of the wind and not subject to the warmth of the sun. Cover the pots with two to three inches of shredded leaves or straw. Cut off the boughs of your Christmas tree and lay them on top of and around the potted perennials to give them extra protection and keep the mulch in place. Avoid placing the pots on a raised location such as a deck as the exposure to the cold air from below can be detrimental.
During late fall, before the ground has frozen, potted perennials can be placed into holes dug in the ground. The soil acts as an insulator to protect the roots. Just remember to remove them in the early spring. If left in the ground too long the roots can begin to grow so much that they will grow through the drainage holes and anchor themselves to the ground. I have placed pots in a protected area from wind, turned them upside down to keep the pots from cracking, then covered them with a combination of wood chips, leaves and pine boughs with much success. Once the weather has warmed a bit I start checking my overturned pots for signs of growth.
Potted perennials can also be stored in a garage or outbuilding, however it has to be a cool location or they will not overwinter properly. Always keep in mind that the tissues of some plants, especially trees and shrubs, are more susceptible to cold weather damage in their youth or the first couple of years after transplantation. It is only when they have reached a certain level of maturity that they are then fully hardy.
Never overwinter perennials in a greenhouse or other warm place as perennials need a period of dormancy which is brought on by cold weather. Perennials in plastic pots can be overwintered outdoors in those pots. Plants in terra cotta or stone pots cannot be overwintered outdoors in them as the pots will crack. Remove the plants from the terra cotta or stone containers and plant them directly into the garden.
As always, Happy Gardening!
More information about gardening and related subjects is available online at www.hort.purdue.edu/ext/garden_pubs The Purdue University Cooperative Extension Service
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