Dressing Plants for Winter

We’re turning on the heat, unpacking our winter sweaters, and looking up our favorite soup recipes. And if we’re gardeners, we may be figuring out the best way to protect our plants for winter. Lately I’ve been seeing ads for rose collars and burlap wraps. Should I buy some?

Many hybrid roses are grafted onto rootstocks bred for hardiness, not pretty flowers. It’s imperative to protect that graft union in very cold weather. If the top half of the plant dies, the roots will send up shoots next spring—we won’t be aware that anything is wrong until our petite pink rose suddenly grows into a huge sprawling shrub with ugly white flowers.

Rose collars are supposed to prevent this from happening. According to the ads, you can “fill collar with mulch to protect delicate hybrid rose grafts from freezing.” Or, as another manufacturer gushes, “Keeps your roses cozy in winter!”

Grafted roses are borderline hardy in much of Colorado, largely because of that bud union. (Shrub roses and rugosa roses are easier to grow because they have their own roots.) Using rose collars to protect our roses sounds like a wonderful idea. But do they work? Yes… but.

And how about those burlap wraps? I don’t grow arborvitae or junipers (allergies, unfortunately), but I do have other conifers in my landscape. Should I give them burlap blankets?

First of all, it makes no sense that rose collars or burlap wraps keep plants from freezing. Coats and sweaters keep us warm because we’re mammals. We produce body heat, and the layers of insulation trap that heat inside. But the amount of heat that plants produce from cellular respiration is so miniscule, it may as well be zero. Plus, this is winter—the plants (even the conifers) are dormant. There is no source of heat inside that wrap.

This sounds logical, but just to make sure, avid gardener Robert Pavlis regularly measured the temperatures around a wrapped yew over the course of a severe Ontario winter. For every set of measurements, the temperature under the wrapping was exactly the same as it was outside the wrapping. You can read about his experiment on his blog, Garden Myths.

So, your roses and evergreens won’t exactly be cozy. Then why use rose collars, or wrap plants in burlap?

There are two good reasons. First, winter desiccation is a significant problem. Our intense, high-altitude sunlight warms the branches. Evergreen leaves transpire, losing water. But the ground is frozen, so replacement water isn’t available. Leaves wilt and die. Bare branches split. Protecting plants from drying winds can help them survive.

At least one rose collar ad mentions this: “Eliminate die back caused by drying out of the canes. Allow moisture in during rains, but prevent erosion of mulch.” Of course, our moisture would come from snow, not rain, but the point is valid. This is a one reason to use winter protection.

On the other hand, too much moisture can rot plants, especially those used to our arid climate. Make sure excess moisture can escape, and don’t use impervious covers on xeric plants.

The other reason is to keep plants cold. With many hardy plants, the problem with cold weather isn’t the risk of freezing. They’re prepared for that. It’s the freeze-thaw-freeze-thaw-freeze cycle we get in a normal Colorado winter. The temperatures drop to the teens—freeze! The sun warms the plant during a 40° day—thaw! A storm moves in—freeze! We get a warm spell—thaw! Sound familiar?

This alternating freezing and thawing is very hard on plants, weakening tissues and causing injury. Furthermore, a prolonged warm spell can fool plants into thinking spring has arrived. They break dormancy far too early—a fatal mistake. Plant covers and rose collars mitigate the extremes of these wild temperature fluctuations.

Rose collars and burlap wraps have their place, but I prefer to select plants adapted to our climate, avoiding the time consuming hassle of covering them. Besides, I don’t like the look of covered plants. If I wanted a plastic and burlap garden, I would have planted one.

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