In the Garden:
A burlap wrap can reduce water loss and wind damage on evergreens, which continue to respire (very slowly) all winter long.
Better Late Than Never
Snow is flying past my windows, and as I watch it coat my weeping birch, I think, "Uh oh." I see that I haven't wrapped the tree trunk yet to protect it from wintering rodents and browsing deer. I intentionally wait until the ground is frozen before installing the guards and mulching, so that the mice and voles will already have found winter sleeping grounds, but now my window of opportunity is narrowing because I need to install tree guards before the snow gets too deep to reach the base of the trees. It's time for some last-minute efforts to help make sure the landscape plants awaken in spring in the best shape possible.
Trees and Shrubs
Any young tree -- in some years, any tree -- left with a bare trunk in winter is an invitation for hungry critters. I use the white plastic coiled tree guards on trees of smallish caliper. Start at the ground and wrap the guard around the trunk, moving upwards. Wrap up to a height that's above the typical snow depth, or at least 2 feet high. If the tree has low branches, and for larger trunks, use the brown paper tree wrap because it's more flexible. You want to make sure the trunk is protected both from rodents burrowing in the snow and from deer passing by. A barrier won't keep the deer from tasting the branches, of course, but it will deter them from sampling the bark.
Tree wrap also protects tree trunks from sunscald, which is caused by the sun heating up the bark during the day and then plunging the bark cells into the deep freeze at night. It's most likely to occur on the south and southwest sides of a tree and during unusually warm days in winter and early spring.
The branches of some trees and shrubs need special protection from cold winter winds and heavy snows. My rhododendrons, false cypress, and any young evergreen get a burlap cocoon. I place wooden stakes around the plant and wrap burlap around the stakes, securing it with twine. You don't necessarily need to cover the top, but do so if possible. The one year I neglected to wrap my false cypress, it lost lots of needles from winter kill.
Once the ground is frozen, it's time to spread winter mulch. If you spread it earlier, the rodents might still be in their underground tunnels and you'll be providing a nice hideout that leads to your tree trunks. Even if the snow has fallen, you can still mulch. Keep it a couple of inches away from the trunks, just to be on the safe side. You're trying to protect the root zone with the mulch, not the trunks.
Wood chips are a good choice for mulch because they don't compact down and restrict air flow around the roots. Plus they will decompose over time and provide organic matter to the soil.
Most types of roses need protection, as well. My rugosa roses and hardy climbing roses fend for themselves, but I mulch the others -- even the hardier ones growing on their own roots (not grafted). The main considerations are to protect the canes from damaging winds; to protect any graft unions, which are the most vulnerable part of the plant; and to keep the soil from warming up prematurely in spring, triggering the plants to begin growing before wintry weather has finished with us. Encircle the plants with stakes and wrap burlap or wire mesh fencing around them; or use commercial plastic cones (only those with ventilation in the top). Then fill the inside of the cylinders with wood chips or hay or straw, as deeply as possible. For grafted roses, first mound the soil up about a foot around the graft, install the wind protection, then fill in with mulch.
A thick layer of evergreen boughs also makes good mulch for roses. I don't recommend using cocoa hulls for winter mulch because in a thick layer they can compact and get slimy.
The biggest threat to perennials is the alternative freezing and thawing temperatures that can heave the crown out of the ground and expose the roots to the cold. Use a loose mulch -- chopped leaves, wood chips, hay, or straw -- to cover the root zones, but don't pile it up on top of the crowns of the plants or they may rot. Plants especially sensitive to rotting in cold, wet soil, such as penstemons, agastaches, lavender, heather, Russian sage, and dianthus, are best protected with gravel mulch if the soil is mostly clay or doesn't drain well.
While you're outside wrapping and mulching, don't be tempted to cut back perennials to neaten things up. Any marginally hardy plants will benefit from the stalks remaining in place to catch the snow and help insulate the crowns. And the birds will appreciate the protective cover and any leftover seeds.
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