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Overwintering Marginal Plants

I keep seeing photos of interesting plants I’d like to grow, but they’re labeled zone 6 and I’m in zone 5. What can I do to successfully overwinter these marginal plants? I’d like to try them, but I don’t want to waste my money.

“Pushing a plant past the limits of its hardiness is not for the average gardener,” says Marie Dvorak of The Planter’s Palette in Winfield, “but plants can sometimes be successfully overwintered by siting them in a special microclimate such as a sheltered southern exposure.” Another tip comes from horticulturist Ann Hancock at Michigan State University, where they are trialing perennials that the English firm Blooms of Bressingham is introducing in the U.S. Hancock explains that the best way to keep perennials that are tender in Zone 5 or that are rated for Zone 6 is to grow them in raised beds with good drainage because poorly drained wet soils will cause the roots to rot. In addition, it is important to check perennial beds for plants that have heaved out of the soil through repeated freezing and thawing. Replace them in the soil and protect with mulch.

One example of a marginally hardy plant that will be getting attention this year is ‘Flamenco’, a new cultivar of Tritoma (Kniphofia, red-hot poker) that has just been named an All-America Selections Winner for 1999. Tritomas should have their foliage tied upright so water does not remain in the crown, said Hancock.


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