It's been a real New England winter this year -- very low temps interspersed with plenty of snow. Since predictions for the end of the week have highs in the single digits, I've been concerned about my container plants.
I'm an urban gardener. I grow almost everything in containers, from clematis and hydrangeas to strawberries and tomatoes. And every fall, I agonize over what I'll try to keep over winter -- and how.
There are several problems -- plants in containers freeze more quickly than those in the ground (and the soil freezes all the way through), plus there's more freezing and thawing because of the lesser amount of soil. Also, terra cotta or clay containers tend to crack from the cold.
There's all sorts of advice out there to help with this, and over the years I've tried just about all of it:
Grouping them together near the house or other structure, with the hardiest plants on the outside, and insulating the grouping with mulch, hay, or piles of leaves. (Or wrapping individual pots with Bubble Wrap.)
Coating the interior of clay pots with waterproof sealant.
Emptying the pots of plants and soil and storing them upside down. New England gardening expert Carol Stocker told me about this one, and it works well for containers in which I grew annual flowers or vegetables and therefore are empty.
Grow hardier plants. Often I read recommendations to stick with plants that are hardy in USDA Zones that are one or two colder than your own (i.e., Zone 4 if you live in Zone 6). This sounds good, but that's not how I choose plants -- I want them for color, for their interesting flowers, because they're new, and for dozens of reasons that have nothing to do with their hardiness.
Move to a protected area. This is what I usually do.But I have lots of pots, and often I run out of space in the garage.
My experience is that some plants always make it and some just don't. I've had better success with shrubs and vines than with perennials. (One exception: daylilies. I've never lost a container-grown daylily.)
Much depends on what a particular winter's weather is like and how much snow cover we get -- and how long it lasts. (Snow has excellent insulating properties.)
As i was thinking about whether I needed to do something, I saw Jeff Gillman's post about some research on this topic. Dr. Gillman is the respected author of the fascinating books "The Truth About Garden Remedies" and "The Truth About Organic Gardening."
In both, he looks at what works and what doesn't. He also writes a quarterly report on new garden research for Garden Rant.
In the most recent edition, he reports on a study at Ohio State University, which tested 30 perennials growing in containers for winter-hardiness. Only one survived. (Sedum 'Matrona,' which I never would have guessed.)
His conclusion is much the same as my experience -- if you've got container plants, get them out of the weather and into an enclosed area such as a shed with a door that closes or a garage.
Guess I'll be piling a few more plants into my garage this afternoon.