How to Protect Your Containers in the Winter
An Alaskan gardener explains how to overwinter container plants.
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by Marion Owen, special to HGTV.com
I sleep and garden in Alaska, a state so vast you can fill it with two Californias, one Texas and top it off with a New Jersey maraschino. Dozens of containers dot my property on Kodiak Island. They're home to perennials, herbs, fruit trees, berry vines, roses and birch trees.
For the most part, northern gardeners chuckle at being assigned climate zones, which are generalizations at best. It's like saying ice cream only comes in vanilla. In Fairbanks, for example, permafrost chills roots while leaves and flowers bask in 90-degree heat. Yet tenacious folks grow corn and dinner-plate dahlias, even if it means lining raised beds and containers with sheets of foam. And as days shorten, gardeners don't give in easily. Here are some tried-and-true tips to help carry your container plants through the winter, no matter what zone you're in:
One of the easiest ways to give containers winter protection is to simply move them into an unheated garage or shed, preferably where temperatures stay above freezing. Avoid storing potted plants in a heated room. To relocate them, use a hand truck or some other means (watch your back!). Check the soil from time to time to be sure it doesn't dry out completely; roots should be moist but not wet.
If you don’t have an unheated protected space, you can leave your containers outside. I'll admit, determining which plants will survive the winter is mostly a matter of trial and error. If you're not sure, slip the plant from its container in the fall, and plant it directly in the garden.
Rita Jo Shoultz, owner of Fritz Creek Gardens in Homer, Alaska, shaves a step. "With so many plants, I bury the whole thing, plant-plus-container, right up to the rim." She finds that hostas, pulmonarias, ajugas, hardy gingers, lamium and other woodland perennials survive winters quite nicely. If, however, you only bury the container halfway, fill in with loose soil or shredded leaves to help them retain moisture.
An evergreen solution
As plant tops wither and die back, Shoultz covers them with evergreen branches, her favorite way to protect plants from repeated freeze-thaw cycles. Lightweight evergreens not only allow light to enter, they permit air and moisture to circulate freely, which prevents crown rot.
Repeated freeze-thaw cycles are also hard on the pots themselves. Plastic becomes increasingly brittle, clay pots crack or shatter; even cement will break if small fissures get filled with water that swells into ice. Although foam containers offer good insulation, older, weathered ones can develop cracks and eventually split.
Plants need water to survive, but too much water in a cold climate can kill. As a general rule, water your plants only until the ground freezes. That said, water can collect and freeze on top of the soil, damaging plants. To prevent a skating rink from forming inside the rim, move your containers away from downspouts or tilt them on their side to allow water to drain off. As a final precaution, fill in excessive freeboard space with soil or mulch to within an inch of the rim.
Safety in numbers
Just as penguins huddle together for warmth, potted plants have a better chance of surviving when grouped together. Julie Riley, horticulture agent for the Cooperative Extension Service in Anchorage, prefers the group method, recommending that you "pack bags of leaves all the way around containers and on top if you can." Keep bags from blowing away by corralling them with chicken wire.
It's a wrap
Many household items can serve as blankets to protect containers from severe winter weather. Here are some ideas, presented from lightest to heaviest protection:
For extreme conditions, your best bet is to follow Paris fashions by dressing your containers in layers. (Layers are always in style.) If your winters are wet as well as cold, add a final layer of plastic on top of the insulation to keep it from getting soggy and heavy. As late winter melts into early spring, keep an eye on the temperature before pulling containers from the ground or removing wraps.
While I might grumble about snow when I'm shoveling the stuff, I appreciate what it does for the garden. Even a thin layer on exposed, open ground reduces winter kill and damage caused by freeze-thaw action. "Although snow does not contain any appreciable quantity of plant nutrients," said J.I. Rodale in my 1959 copy of The Encyclopedia of Organic Gardening, "it often acts as a natural buffer or mulch." In some cases, he added, the gradual thawing of snow improves the soil's texture, much like the burrowing action of earthworms, bacteria and fungi.
While wrapping containers with blankets or bagged leaves might not seem like attractive solutions, they give your plants a fighting chance, which saves you from buying new plants next season.
I find many wonderful containers at local restaurants and bakeries. They are the one- to five-gallon plastic containers recycled from the food service industry. Frosting, mashed potato flakes, chocolate chips and all manner of products are stored in these re-useable tubs, complete with handles and lids. In addition to plant pots, I use them as tool totes, weed buckets and for storing bone meal, seed starting mix, and bird seed. What's more, they're free for the asking!
My favorite plant container is a large, black, indestructible tub used for commercial halibut fishing. It measures a good 30 inches across the top and as deep; it doesn't fade in the sunlight or crack in the cold. Made of a tough, but flexible polyethylene, you can drop these tubs, roll them, pick them up with a hand truck. What's more, they're fun to paint. I don't know how I'd garden without them!
One last tip: If anyone teases you about your hodge-podge of containers and happens to ask, "Hey, what zone are you in, anyway"? Just smile back and say, "The ozone!"
--Marion Owen is co-author of Chicken Soup for the Gardener's Soul.
Shari transforms a teen's plain bedroom into a tropical paradise.