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Garden Q&A: Buds in the winter and how to keep potted perennials through the cold

Leatherleaf viburnum buds emerge in winter but don't bloom until the spring. - Original Credit: For The Baltimore Sun
Leatherleaf viburnum buds emerge in winter but don't bloom until the spring. - Original Credit: For The Baltimore Sun(Handout / HANDOUT)

This shrub looks like it is about to bloom — in winter. What is it? The leaves are about the same size as rhododendrons, but not as smooth. The flower buds are different.

Leatherleaf viburnum has coarse, shiny leaves, that are virtually evergreen, which is rare for a viburnum. The flowers open in spring — typical for a viburnum. The leatherleaf’s flowers are off white and not showy but numerous.

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The plump unopened buds add good winter interest, promising of spring. Growing to 10 feet or more, Viburnum rhytidophyllum does well in a shrub border, either massed or mixed for contrast with rhododendrons and other shrubs. With no serious disease or pest issues, it can be a handy landscape addition since it can take heavy shade. It is not native.

I need to protect some potted perennials from the cold this winter. No ground is available to “heel-in” or sink the pots into the ground, but I have a totally dark, unheated shed attached to the house that is insulated, where the temperature is over 50 degrees during the day. Is that too warm? What would be a happy solution for my situation?

It sounds as if the shed would be too warm to ensure unbroken dormancy all winter. Overwintered perennials that break dormancy and sprout too early risk pest outbreaks (such as aphid). They would also need light, air circulation, and more frequent watering if dormancy broke and growth resumed. They would lose some cold-hardiness at that point, so a drastic temperature swing from a late freeze could cause damage.

Overwintering outside with added protection around the roots is best. That way, they can stay “on schedule” to break dormancy when they should and also will dry out less often. Insulate roots by mounding-up material around the pots; the larger the mass, the slower it will change temperature or reach extreme temperatures. Mulch, sawdust, straw bales, bagged soil — anything you can “plant” them in above-ground will help. During thaws or warm spells, check the pots for moisture. Plant nurseries often overwinter inventory this way, and winter damage is typically minimal.

University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Maryland’s Gardening Experts” to send questions and photos.

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