Over Wintering Perennials in Containers

There was a time that the only type of plant you would see in a container, growing outdoors, was an annual.  These days, anything from perennial flowers to trees and shrubs  are being used in containers to beautify outdoor spaces.  Yes, these plants can be treated like annuals and be replaced the next season, however I find it impossible to let something die that, with the right care, can grow back next spring.  Because of this, now is the time to consider the options of over wintering these pots so that the plants in them can survive the winter to come back and beautify our outdoor spaces next year.

Perennial plants in pots need protection during the winter months because their root system is being kept above ground.  If these same perennials were planted in the ground, they would have the advantage of the soil to help insulate and protect their root system.  When kept above ground, that insulating factor is no longer in existence, making the roots vulnerable to extreme winter temperatures.

To start the overwintering process, make sure your plants have plenty of moisture.  Frost penetrates deeper into the air spaces of dry soil than moist soil because water has filled up the air pockets.  Allow the plants to enter their dormant stage by exposing them to several nights of freezing temperatures before putting them away for the winter.

If you have the space in your garden, dig a hole the size of the pot.  Place the pot in the hole, making sure the depth is up to the rim.  Backfill the hole with soil then cover the plant crown and pot with a thick layer of mulch.  You can use straw or leaves as the mulch cover.  I like to go a bit further and cover my mulch with pine boughs to keep the mulch in place.  The root ball can be removed from the pot and planted in the ground and mulched.  Clean the pot and store it indoors for the winter.

You can also group your pots in an inside corner of a building, on dirt, not concrete and mulch them heavily, placing mulch in between the pots. Place the cold hardiest plants along the outside of the grouping with those that need a bit more protection to the inside.  An east or north side is best for this practice.  Straw bales can be used along the outside edge to protect the grouping from winter winds.

I use a few clay pots for some hosta’s and have found that, once the foliage has died,  turning them upside down in my garden and loosening the soil from the pot keeps the pots from cracking.  The inside of the pot can also be painted with pool paint which will keep it from absorbing moisture from the soil. I then mulch them heavily with leaves, straw and pine boughs.  Once temperatures have started to warm up a bit in the spring, check the overturned pots for signs of growth.  When the green foliage appears, it’s time to turn them over.

Your containers can also be moved into an unheated building such as a garage or shed.  If you do this, remember to check on them occasionally to see if they need a bit of water.

As always, Happy Gardening!

More information about gardening and related subjects can be found online.  The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.