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March Mania

No need to let go of potted plants this winter

If outdoor pots contain multiple geraniums, they are best removed and potted individually for indoor growth and can be returned outside in the spring. Michael Vosburg / Forum Photo Editor1 / 3
Don Kinzler, Growing Together and Fielding Questions columnist.2 / 3
Outdoor container plants like mandevilla can be wintered indoors and returned to decks and patios in the spring. Michael Vosburg / Forum Photo Editor3 / 3

What's your reaction to fall's first frost? Do the neighbors question whether all the white sheets in your yard are Halloween decorations or just you covering your tomatoes and geraniums again?

Do you struggle to squeeze into your car because any extra space in the garage is filled with trays of yet-to-ripen tomatoes and you've moved all the still-beautiful pots and planters into the garage on frosty nights, because you might want to winter some indoors?

Maybe it's because we hate to see the gardening season end. Maybe my wife, Mary, should serenade me with "Let It Go" as I haul leaf-dropping potted plants in through the kitchen.

Some outdoor container plants winter beautifully indoors, not only saving money as we return them outdoors next spring, but giving our indoor space some winter excitement. Plants that can be successfully wintered if not allowed to freeze include geranium, coleus, hibiscus, mandevilla, dipladenia, thunbergia black-eyed Susan vine, sweet potato vine and fibrous-rooted begonia.

Hibiscus, mandevilla and dipladenia: These tropical natives are easily injured by temperatures below 45 to 50 degrees. Before bringing indoors, rinse plants with a gentle stream of water to dislodge hitchhiking aphids and mites. Spraying with insecticidal soap, sold at garden centers, is a good precaution.

If quite large, prune plants to a manageable size. Locate in the sunniest indoor location possible by patio doors, large windows or in a sunroom. Because mites and aphids are almost guaranteed, I've had great success applying systemic houseplant insecticide granules to the soil, which protects plants from the inside out.

Short days and decreasing light signal plants to slow down. To follow this natural rhythm, decrease watering frequency, which imitates the dry season of the tropics. Water only when soil is quite dry. Reduce fertilizing to once a month at half strength. Repotting should wait until late winter.

Leaves often turn yellow and drop, which is normal, and they'll regrow when necessary. In the meantime, water sparingly. Don't push the plants to bloom indoors if they don't want to.

By March, lengthening days will signal plants to resume growth. This is the time to repot, increasing pot size only slightly, using a potting mix high in peat moss. Prune away spindly winter growth to encourage fresh branching. Begin fertilizing every two weeks, and increase watering as plants begin new growth.

When spring night temperatures remain consistently above 50 degrees, plants can be moved back outdoors.

Geraniums: Fresh plants can be propagated from tip cuttings 3 inches long rooted in a mixture of peat and sand or peat and vermiculite. The "mother" plants can be dug out of planters, cut back to 3 inches above soil level, and potted individually into 4-inch diameter pots for growing on sunny windowsills or under fluorescent lights.

Water geraniums sparingly during winter, fertilizing once a month. In early March, cut winter's spindly growth back to 3 inches above soil level once more to encourage well-branched, stocky growth, as lengthening days trigger new growth. Begin fertilizing every two weeks.

Coleus, sweet potato vine, thunbergia and fibrous begonia: For fresh plants, propagate tip cuttings in water or preferably in media such as vermiculite. When well-rooted, pot into 4-inch pots. Mother plants can be repotted and brought indoors after trimming back to a manageable size. Grow in sunny windows or under lights. In March, trim back to encourage compact, well-branched plants.

Don Kinzler, a lifelong gardener, worked as an NDSU Extension horticulturist and owned Kinzler's Greenhouse in Fargo. Readers can reach him at