When it comes to hydrangeas, I’m certifiably loony. Or, at least, I used to be. The source of my obsession was a variegated hydrangea. I bought it in full flower, and the azure, lacecap blooms were simply stunning against the backdrop of broad, spade-shaped leaves edged with creamy white. Then winter hit and it died to the ground. New shoots burst forth in spring, adorned with luscious foliage, but no blooms appeared. Ditto the next spring. And the next. Apparently the plant was root-hardy here, but its stems and flower buds—which form on year-old growth—were not. In my USDA Hardiness Zone 6 Connecticut garden, Old Man Winter prevailed.
But it got me thinking that if I kept my variegated hydrangea (Hydrangea macrophylla‘Tricolor’) warmer, its stems and buds might survive. So I decided to cover the plant in winter. I bought one of those homely-looking Styrofoam cones sold to protect tea roses in winter, capped the hydrangea, and covered that with a layer of shredded leaf mulch and pine boughs. Then I waited until the next summer when—lo and behold—the hydrangea flowered.
Emboldened by success, I started experimenting with other marginally hardy plants, using everything from small glass domes to homemade, doghouse-sized plastic greenhouses. I soon realized winter cover-ups could provide an extra zone or more of warmth. I’ve used these devices to help late-season transplants get established, protect recently transplanted evergreens, and coddle a few choice perennials that would otherwise never survive winters in my garden. There’s nothing complicated about it. I rarely spend more than 15 minutes prepping a plant for winter, and unveiling it for spring takes even less time. My methods aren’t foolproof. There’s still a casualty or two every season. But even with occasional losses, my efforts are repaid several times over each year.
PROTECT TENDER PLANTS WITH WATER, MULCH, AND SHELTER
Everyone knows that plants die if winter temperatures are too frigid for them to endure. But severe weather can pose a threat even to hardy plants. An early-season burst of bitter cold can shatter the cells of woody plants that haven’t yet hardened off. Later in the season, those same plants could march through a similar cold snap in stride. Deeper into winter, cold, dry winds can draw the life from conifers or broad-leaved evergreens. Even warm spells can be perilous. High temperatures can evaporate the last reserves of moisture from the transpiring leaves of evergreens whose roots, locked in frozen ground, are unable to draw replenishing moisture from the soil.
Most hardy perennials could sleep through winter peacefully if tucked under a thick blanket of snow. But where snowfall is iffy, exposure to Jack Frost’s full force may kill marginally hardy plants. In poorly draining soils, winter wet can rot the crown of hardy perennials. And the churning freeze-thaw cycles of early spring can easily heave plants—roots and all—from the ground. To complicate matters further, the tissues of some plants, particularly trees and shrubs, are more susceptible to cold temperatures in their youth or their first year or two after transplanting. Only when they’ve reached a certain level of maturity are they fully hardy.
My garden is subject to just about every one of those threats. So, to prepare marginally hardy or recently planted perennials, trees, and shrubs for winter, I make sure at-risk plants are deeply watered before the ground freezes. In addition, any recently transplanted or marginally hardy evergreens get a spray of an anti-transpirant, like Wilt-Pruf, to seal the microscopic openings in their leaves. When the ground has frozen, I give new plants—even those rated bone-hardy for my garden—a 2- to 4-inch blanket of mulch, either ground bark or, preferably, shredded leaves. I also use pine boughs or branches cut from the Christmas tree. These make an excellent, airy mulch for young hellebores or any fledgling evergreen perennial because they help moderate temperature changes and offer protection from the winter wind and sun.
Plants in need of special coddling—anything unlikely to survive winter’s cold and wet—should be tucked into a custom, seasonal shelter before cold weather settles in, usually about late November in my garden. It doesn’t have to be elaborate. I’ve used overturned plastic pots, lengths of burlap, shredded leaves, even a heavy-duty paper bag. Unless you make the effort to build an artistic shelter, chances are that an array of protected plants is going to look like a hastily abandoned campground. But I can live with the less-than-good looks for a year or two until a newly planted tree or shrub is well-established. Even so, any plantings that will need long-term coddling shouldn’t be positioned prominently in the stark winter landscape. To avoid aesthetic crises, I tuck my tender treasures at the bottom of a gentle slope in the backyard, where they can’t be seen from the house.