Guidelines for overwintering plants

Guidelines for overwintering plants

by C.L. Fornari

In October, the temperatures fall steadily in the Northeast. Yet many are unwilling to let their summer annuals die and contemplate bringing them indoors for the winter. The plants are still beautiful after all, and it's more economical to keep them for next year.

New England professional gardeners say overwintering some varieties is a good idea, but others may not keep well indoors. Maggie Oldfield, owner of highly rated Thayer Nursery in Milton, Mass., suggests bringing in some tropical plants. "The giant elephant ears can be kept in a pot and treated as a houseplant, and the tropical hibiscus does well," she says.

These plants should be put in a south or west-facing window to provide enough light. Citrus plants, such as Meyer lemon (Citrus x meyeri), rosemary (Rosmarinus) and bay (Laurus nobilis), also need as much sun as possible. The popular summer-flowering mandevilla (Mandevilla) vines can be easily kept alive in a bright location, but unless you have a greenhouse, it won't receive enough light to trigger flowering until late in the following summer. This is one tropical plant that is better purchased already flowering every spring.

Judi Lipson-Rubin, owner of highly rated Moodscapes LLC in Arlington, Mass., says that some of her clients try to save a few annuals from year to year. "I think that the standard geraniums are the plant that's most commonly kept through the winter," she says. Geraniums (Pelargonium) continue to bloom and look good in a sunny window.

While some annuals and tropical plants need to be kept in south-facing windows, others can be stored where there is little or no light at all. In general, plants with very thick stems or tubers can be kept dormant in cool, dark locations and will come back the following spring.

Those geraniums that bloom in kitchen windows can also be left to sleep in a dark, cool space along with angel's trumpet (Brugmansia), bananas (Musa or Ensete), gingers (Zingiber officinale), cannas (Canna) and caladiums (Caladium). Put these in the basement in October and move them outside once the danger of frost has passed in spring.

Oldfield and Lipson-Rubin agree that there are many annuals that shouldn't be kept through the winter. "I wouldn't bother overwintering common annuals such as impatiens or marigolds," Oldfield says. "They're more trouble than they're worth because they get leggy and are prone to bugs."

In order to avoid bringing insects indoors, Lipson-Rubin advises treating plants while they're still outside by spraying them with insecticidal soap to kill any bugs.

General guidelines for overwintering plants are:

  • Don't fertilize from October through January. The plants aren't actively growing so they don't need extra nutrients.
  • Keep most plants on the dry side. Exceptions include hibiscus (Hibiscus rosa-sinensis), papyrus (Cyperus) and citrus, which should be kept evenly moist.
  • If leaves or the floor under the plant become sticky, this indicates an insect infestation. Spray with horticultural oil or insecticidal soap. Always read and follow the label directions.

C.L. Fornari is a writer, gardening expert, professional speaker and radio host who is dedicated to getting you into the garden. The Osterville, Mass., resident is a member of the Perennial Plant Association, American Plant Propagators Society, National Speakers Association and Garden Writers of America.

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