Are your shrubs brown? Blame the roller-coaster winter weather

Contributing Garden WriterMay 2, 2014 

  • TIPS

    A few tips for coping with winter damage:

    Match the plant to the site. William Fountain, of the University of Kentucky's College of Agriculture, suggests taking special care when planning where to plant. He says, "Broadleaf evergreens must be sited in areas that are protected from the winter sun and drying winds. As we look at what is native in Central Kentucky, specifically what has stood the test of time over the last 12,000 years, since the end of the last ice age, we do not see many native broadleaf evergreens. This should be a hint to those of us who love and study our native flora and fauna."

    Pay attention to plant hardiness. "We live in the transition zone between North and South, says Jaime Dockery of the Fayette County Cooperative Extension Service. "People will always long for the exotic Southern look of broadleaf evergreens and be tempted to plant things that are not reliable here. Our long string of mild winters lilted us into thinking we were in southern Tennessee. Not surprisingly, I have seen no damage to plants native to Kentucky." Give due consideration to USDA hardiness zone recommendations. Kentucky is mostly in USDA hardiness zones 6a and 6b; some parts, mostly in Western Kentucky, are in 7a. See all hardiness zones at Planthardiness.ars.usda.gov.

    Hedge your bets by growing healthy native plants. Todd Rounsaville, native plant curator at The Arboretum, reminds gardeners that environmentally stressed plants are more susceptible to the additional threat of freezing weather, and therefore he advocates choosing plants that are adapted to our region. "Be willing to source and grow local native species," he says, "or accept that exotic plants, like Asian magnolias, are going to get their flowers whacked by frost most years."

  • DEALING WITH DIEBACK

    Richard Weber, owner of Springhouse Garden, offers some instruction about dealing with dieback in three particularly popular landscape plants:

    Cherry laurel. Evergreen laurels like "Otto Luyken" and "Schip" have been widely planted, mainly as hedges, for about 15 years. They can reach 6 to 8 feet in height, but are only marginally hardy in USDA Zone 6, which covers Kentucky. Often their healthy root system allows sprouts to emerge close to the ground. Trim away dead wood, and you should have decent regrowth by the end of the summer.

    Nandina. Commonly called "heavenly bamboo," nandina if left untrimmed can grow leggy and unsightly, producing clusters of beautiful but toxic red berries at the tops of 7-foot branches. An exotic plant, it is somewhat invasive, so cutting back is a good idea. Don't expect berries to appear this year, as flowers appear on old wood.

    Crape myrtle. These popular accent or row shrubs can be cut down to ground-level "nubs" and be expected to sprout vigorously. Prune new growth to just a few sprouts, which will give the tree a pleasant structure; expect blooms to grow on new growth.

Knock on wood, winter finally seems to be over. The long, constant freeze, however, has left its mark on many Central Kentucky landscapes, turning broadleaf evergreens brown, leaving bud-bare branches brittle and flash-freezing away emerging early spring blooms with temperatures fluctuating from balmy to frosty.

What's the general damage report and prognosis for recovery and rejuvenation?

As the weather warms up and new growth emerges (or not), Richard Weber, who founded Springhouse Gardens in Jessamine County about 20 years ago, has some reassuring advice: "Be patient, don't despair, and let the plants tell you how much they need to be cut back."

Many affected trees and shrubs are still struggling to bud out and some are even recovering from the ground up, so even if it seems your plant is a goner, give it a bit more time.

Todd Rounsaville, native plant curator at The Arboretum, the state botanical garden on Alumni Drive in Lexington, points out that "the prolonged winter delayed 'typical' phenology so we have observed many plants leafing out or flowering later than normal."

Fayette County Cooperative Extension Service's horticulture agent, Jaime Dockery, adds, "See where the new growth occurs over the next month or so, and then prune out the dead accordingly."

There are many reasons why plant dieback occurs, including damage from disease, animals, insects and salt; breakage from the weight of ice or snow; and being only marginally suited for the site or USDA cold or heat hardiness zone in which they're planted. Recently acquired plants that are not yet established are also more susceptible.

"Trees usually die as a result of multiple stresses, and something like cold temperatures could just finish off an unhealthy tree," Rounsaville says.

An advocate for planting native species, he says the winter had little effect on The Arboretum's native collections.

Jesse Dahl, The Arboretum's horticulturist, lists plants that showed damage to include less hardy or exotic species like cherry laurel, crape myrtle, lavender, blackberries, magnolias and chaste tree. He notes that plants like crape myrtle, which is marginally hardy in Kentucky, can be expected to die back in a stressful winter every 10 to 15 years, but many will grow back from the roots.

William Fountain, an extension professor of arboriculture and landscape at the University of Kentucky's College of Agriculture, adds to the list of injured plants in our region: evergreen holly, boxwood, Mahonia holly, English ivy, nandina, firethorn, osmanthus and arborvitae.

What made this winter exceptionally hard on broadleaf evergreens like magnolias, some hollies, rhododendrons, azaleas and boxwood was not so much temperature extremes as it was long exposures to freezing weather.

"This winter, the water in the soil froze deeper and stayed frozen for longer periods than we have experienced over the last decade," Fountain says. "The bright winter sun warmed up the foliage, and because of the low humidity and drying wind, the foliage lost water.

"Unfortunately, the plants were not able to absorb the frozen water from the soil or move it through the frozen stems; this strong pull of water in the leaves left air pockets in the plants' conductive tissues, and as spring began the leaves and some stems dried out and have died."

More simply stated, Weber says, the plants were "freeze-dried."

Susan Smith-Durisek is a master gardener and writer from Lexington. Email: durisek@aol.com. Blog: gardening.bloginky.com.

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