The Cold, Hard Facts Find out the secrets of winter survival for potted plants. (Continued from Page 1) By Susan Morgan
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When it comes to containers for the winter, the bigger the better. The surrounding soil helps provide insulation for plant roots. --photo courtesy of Denver Botanic Gardens
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When choosing a pot, bigger is better. "The larger the volume of the container, the better off the plant will be," says Mathers. The soil in a 15-gallon container will insulate the roots better than that in a one-gallon pot. The smaller container will freeze faster. A good rule of thumb: select a larger-sized pot that also has a thickness of one inch or more. Also, smaller pots dry out more quickly than large pots. Plant the container as early as possible in order to allow plants to harden off. If plants are healthy and go into winter with mature roots, they have a much better chance to harden off and, as a result, will tolerate winter stress much better.One trick: Select container plants that are hardy to 20 degrees, or two zones, cooler than your hardiness zone. Hardy dwarf conifers, evergreens, ornamental grasses and trees or shrubs with interesting habits or bark colors are great for adding winter interest. If possible, place pots with these plants near a window or front door where they'll be easily seen.
Winter Container SelectionThe climate in your area determines what types of pots will do best in winter. Untreated porous containers, such as terra cotta and ceramic, tend to crack and break with freezing and thawing. In his USDA Zone 4 garden, Ray Mims, director of horticulture at the Denver Botanic Gardens, likes the look of his large terra-cotta pots and wants to use them all year long. So he treats the interior of his pots with pool paint. The coat of pool paint helps to prevent moisture from entering the porous surface and causing cracks from freezing and thawing.
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Large-sized containers, like this whiskey barrel, can help to protect plant roots in cold temperatures. Make sure to select the right type of container suitable for overwintering container plants in your climate.
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Wood containers can be very durable, depending on wood type and exposure to the elements. Non-porous containers, like concrete, plastic and metal containers, are great for their ability to withstand the elements. However, concrete and metal containers can be heavy and awkward to move once set in place. Plastic pots have the potential to crack over a period of time. Foam or resin pots come in a variety of looks and can be a lightweight alternative to concrete and metal. When using lightweight plastic, foam or resin pots, top-heavy plants can topple over when hit with strong wind, so be careful to avoid causing winter injury to plants.Be wary of using thin-walled pots and hanging baskets. The insulation in these containers may not be enough to protect the root zone. Plus, hanging baskets tend to dry out faster than their ground-level counterparts. If possible, avoid using saucers; collected water can freeze. Raise your pots on feet to provide good drainage.
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