Extension Master GardenerSM Volunteers of Buncombe County

freeze

Protecting Your Woody Plants from Winter’s Wrath

In October, the NOAA (National Oceanic and Atmospheric Administration) forecast a warmer than normal winter for our area. That’s not good news for us gardeners, or for our woody plants! 

Why warmer weather isn’t better
Our shrubs and trees struggled all summer—and now into the fall—with higher-than-normal temperatures and lower-than-normal moisture. Once cooler weather arrives, even short increases in temperature can cause buds to break dormancy. And lower-than-normal cold snaps that accompany our increasingly irregular weather make things worse.

Which woody plants are most vulnerable?
Plants aren’t equally sturdy. Make sure you know what shrubs and trees are in your landscape, as well as their specific requirements. Many popular landscape choices are only marginally cold hardy here in the mountains and your terrain has a lot to do with cold hardiness. Cold air settles in low-lying areas of your yard. Whether a plant is on the north versus south-facing side of your home and has or doesn’t have protection from winds all affect how your plants fare. Evidence is mounting that woody plants with less chlorophyll (green) associated with the foliage—those that are variegated, gold, or purple—are less vigorous than all-green parent species.

Hinoki Cypress_Bark Split from Freeze-Thaw Cycle
Bark split on Hinoki Cypress from freeze-thaw cycle.

What can you do?
To protect your plants from those freeze-thaw cycles—as well as the sunburn, wind, snow, and ice that really do the damage, particularly at higher elevations—you need to provide some additional layers. For plant roots, a good layer of mulch is an appropriate defense. Mulch doesn’t keep the roots warm, but it does protect them from temperature extremes that come with the ground freezing then thawing.

Similarly, protect the upper part of a tender plant by surrounding it with a “blanket.” Drive stakes into the ground around the plant and staple burlap to the stakes. Stuff the spaces between the branches with pine straw. The intent is to keep the plant cold on warm days, rather than warm on cold days. This keeps dormant plants dormant! Avoid using plastic, which traps heat, causing temperatures to rise well above the temperature of the surrounding air.

For evergreens, burlap may help protect from sun- and windburn. Anti-desiccant sprays purport to provide protection, but it may be short-lived. Making sure the roots are well-watered is a better plan to prevent woody plant loss.

Article written by Glenn Palmer, Extension Master Gardener Volunteer.

Your Shrubbery Might Enjoy a Blanket

hardy-gardenia-with-winter-scorch

With all the vagaries of our weather in recent years, my winter forecast is that it will be either warmer than normal or lots colder, leaning toward the latter. In either case, it would be wise to survey your landscape to see where some protection might be a good investment.

The wisest approach is to select hardy Zone 5 plants for your landscape, then place them in a site that will take advantage of the terrain—or perhaps consider buildings for additional protection. South-facing slopes are great because of sun all year long, with cold air drifting downhill. In front of a stone wall is also an option because the wall retains heat.

Cold damage takes different forms and affects foliage, buds, limbs, and trunks in different ways. Often it’s not the lowest temperature that does the damage, but instead, the duration and timing of cold weather.

Boxwood in the snowThe 2007 Easter Freeze came after a prolonged warm spell, long enough to convince some plant species, like Japanese Maples, that spring had already arrived. Even short variations in temperatures can cause buds to break dormancy and lose their hardiness.

For the roots, a good layer of mulch is the appropriate defense. Mulch doesn’t keep the soil warmer but it does slow the freeze-thaw cycles. Once the soil gets cold it stays cold.

You can protect the upper part of a tender plant by surroundings it with a blanket. To do this, drive stakes into the ground around the plant and staple burlap to the stakes as a curtain. Gently stuff the spaces between the branches and the burlap with straw. The intent is to keep the plant cool on warm days, not warm on cool days, which is why burlap is better than plastic. Burlap breathes, keeping the temperature more in line with the ambient, eliminating sudden, short periods of heat. Plastic, whether black or clear, traps the air and allows it to swing above ambient for short periods of time.

Leyland-cypress-with-winter-colorThe same concept can be used to protect evergreen plants against sun or wind burn. Waxy chemical sprays on the leaves can also help prevent desiccation from the wind. This is particularly appropriate for Rhododendrons in windy locations.

To help prevent snow or ice from bending long, pliant branches on a tree or shrub, one can wrap the plant with tape or twine, like a Christmas tree.

Written by Glenn Palmer, originally published in the Asheville Citizen Times.

Heads up! Keep your eyes open for winter plant damage.

winter-gardenAs you make your early garden rounds this spring, keep in mind that our plants, particularly the woody ones, have experienced two very atypical growing seasons. First, a long, moist summer that produced copious amounts of large needles and leaves, along with a bountiful harvest of cones, nuts and fruits. That was followed by an on-again, off-again fall that ended in February with several icy, deep freezes.

Although sap does contain an “antifreeze,” many plants weren’t prepared. Expect to see some damage as a result, along with potential harm from salt.

winter-injuryEvergreens will show the results of desiccation, much like a drought: brown tips and edges, particularly on the windward side. Sub-lethal damage may also cause pigments to change. Green leaves become yellowish, reddish, or purple. Not good, but Mother Nature can handle it.

A later freeze can be even worse. Trees, like peaches, or even some apples, will have met their chilling requirement and decided that spring has arrived. They put out buds and then, suddenly, the buds are lost.

Ice_DamageIce or snow load may have broken branches. Prune them back until there’s a side branch positioned in your preferred direction. Keep your eyes open for later adventitious buds and sprouts from the damaged branch. Remove all of those that don’t contribute to the shape you’re seeking. If you let them grow, they’ll create a tangled mess in the future.

With your herbaceous plants—those perennial flowers—hopefully they were mulched heavily enough to be insulated from temperature swings. If they’re “hardy”, once frozen, they’ve stayed frozen. It’s the chronic freezing/thawing that creates issues.

Keep in mind that different species, or different varieties of the same species, may react differently. A good example is the Japanese maple.

Also, location can create micro climates: north side of a house can be quite different from southern exposure..

One last note: A deformity may not show up until after several years of growth. You might add a “heads-up” note to your garden journal’s spring pages as a reminder.

P.S. All of that vegetative growth has now dried and is ripe for combustion. Put a high priority on getting that cleaned up. Pay particular attention to the spaces under wooden decks, porches and stairways where it could serve as kindling for a house fire.

Article written by Glenn Palmer, Extension Master Gardener Volunteer.

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Buncombe County Extension Office
49 Mount Carmel Road
Asheville, NC 28806
Helpline 828-255-5522

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