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Prepare Now for Frost

Leaving container plants out puts your plants at risk

As you’re prepping your gardens and landscape for winter, don’t forget your container plants. A pot offers nowhere near the protection of the ground, and freezing temperatures are just around the corner.

Cold spells are likely to kill many species of plants growing in above-ground containers, because the roots are not as cold-hardy as the stems, branches and twigs.

Japanese hollies growing in the ground can survive a Maryland winter; grown in above-ground containers, however, those same plants will probably die. Roots of Japanese hollies die when the temperature of the surrounding soil drops below 21 degrees. When temperatures drop down to the teens, the temperature of the rooting medium will also drop within a few hours, killing the roots.

Some ornamental plants — including junipers, azaleas, pine and spruce trees — have cold-hardy roots that can tolerate temperatures as low as negative 14 degrees. But even these plants can be killed when grown in above-ground containers — not by cold but by drought. Home gardeners tend to forget to irrigate plants during the winter months, and the rooting medium quickly dries out.

Protect your container plants by grouping them together near the foundation of the house. Next, mulch the containers heavily with one to two inches of sopping wet bark mulch. Cover the wet mulch with clear plastic to create a one-plant greenhouse. Then remember to irrigate the rooting medium at least twice a month all winter long.

If you do commit to keeping your container plants alive, you’ll also need to select containers that can overwinter. Terra cotta pots will most likely crack and should only be used indoors in cold months. If used outdoors, they should be emptied now, in the fall, and either covered or turned upside down to prevent them from collecting rain, freezing and cracking.

The best containers to use for patio and balcony gardens are made of vinyl, fiberglass, cement, wood or steel.

Ask Dr. Gouin your questions at [email protected]. All questions will appear in Bay Weekly. Please include your name and address.

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