Weathering The Winter: Winter Preparation

Winter in northern climates can have devastating effects on plants. Possible damage includes frost heaving, sun scald on thin-barked trees, browning foliage, flower bud death or injury, or root death.

Many landscape managers turn to overwintering to keep plants dormant while protecting them from severe cold and excess transpiration. "There is a significant range of temperature that the plant can survive given it has enough time to go through the chemical processing before winter," said Steven Rodie, associate professor/landscape horticulture specialist, University of Nebraska, Lincoln, Neb. "The healthier the plant is in the summer and through the end of fall, the better it will adapt to the process to get ready for winter."

In any climate, if landscape contractors neglect to prepare plants for winter, they may find dead or damaged material on their clients’ properties. And no landscape is safe – both new and established plantings can become winter’s prey. "Once new landscaping is in for two or three years, many people think it’s going to take care of itself," said Jeffrey Skelton, landscape architect, Frank Otte Landscape & Design, Louisville, Ky. "But plant loss and severe damage is done to existing material that has been in for several years."

PLANT INJURIES. The extent of winter injury can be difficult to determine and may only be exhibited as delayed bud development or slightly reduced growth. Other times, plant injuries are more obvious. "The biggest problem is the drying out of the plant, which typically means you get dieback and the tree can’t support whatever grew the year before," Rodie said. "You can also get some root death. Overall, you can lose some of the new growth. And any time a plant is in stress, this also opens up bug infestations and diseases."

Ohio State University extension reports the two main types of winter injury are freeze damage, which occurs when temperatures decrease rapidly and plant cells freeze, rupture and die, and desiccation, which occurs when evergreen plants lose water to the atmosphere faster than the roots can absorb and replace it. On needle evergreens, desiccation injury shows up as yellowing or browning needles during winter or early spring, and on broadleaf evergreens, typical injury is scorched or brown foliage, according to Bruce Spangenberg, extension educator, horticulture, University of Illinois, Urbana, Ill.

PROTECTION STRATEGIES. Preparing material for winter often involves mulching, watering, applying chemicals, fertilizers or burlap wrap.

Generally, contractors include these overwintering services as part of landscape maintenance and include charges as part of regular maintenance fees. Skelton said his company charges according to time and materials. The average overwintering job, he reported, takes two or three people working two to three hours.

Here are some common overwintering tasks and how to best complete them.

Mulching. A blanket of mulch maintains a more even soil temperature and retains soil moisture, helping to reduce plant loss and injury from frost heaving. Mulching is ideal for every kind of plant, Rodie enthused.

"If the mulch is organic, it will break down and amend the soil," he said, adding that he recommends peat moss, compost or wood chips, which break down over time. Rodie suggests putting down a 2- to 3-inch layer of organic mulch.

Peggy Campbell, director of education, Molbak’s, Woodinville, Wash., recommends compost mulch to prepare landscapes for Pacific Northwest winters. Compost mulch helps prevent pansy diseases, which tend to be a problem in the region, she said.

Generally, mulching should be done before the first chance of freezing, Rodie said. "For us, this is probably in mid- to late October, when the irrigation systems are turned off, but there are still warm, windy days and a lot of sunshine after this," he explained. "If you wait to mulch until the ground is frozen, getting water into the root systems is more difficult to do."

Ben Lowell, co-owner, BJL Landscape, Denville, N.J., always mulches recently planted material before winter arrives. "Other than that, we give clients detailed care information, and if there are problems with the plants, we tell them to call us," Lowell said.

Watering. An effective way to slow desiccation is to make sure plants get plenty of water in the fall, which will also encourage growth. "Most residential clients think plant growth stops totally (in winter)," said Greg Fracker, co-owner, BJL Landscape. "While there is no growth above ground, the plant is still growing below ground."

Plants must enter winter with enough moisture in the ground, especially conifers or broadleaf evergreens, Rodie said. "We had a severe drought [in Nebraska] last year through the fall and winter, and you can see damage even on plants that have been in the ground for four or five years," he said.

Irrigation systems often do not adequately meet the water needs of the material, Rodie noted. "Many times, contractors put in spray irrigation as opposed to drip, but I don’t think the spray can really soak the root ball as well as it needs to be," he remarked. "The ideal situation is to walk from plant to plant and directly saturate with a gallon or 2 at the roots."

While retaining soil moisture is important, soil should not be soggy. Excessive moisture may lead to root rot, which can be fatal to perennials, Rodie said.

Antitranspirants. Because soil moisture in winter can freeze, plant roots cannot absorb what is lost and the foliage desiccates, turns browns and can drop. Applying an antitranspirant reduces damage to foliage. This can be especially effective in windy sites, Rodie reported.

"Antitranspirants reduce some of the moisture loss from conifers and broadleaf evergreens, especially when they are first planted," he said. "I’ve also seen people put up a sheet of burlap with stakes to cut the wind down. The sheet of burlap forms a wall and cuts the wind."

Lowell uses either an antitranspirant or burlap to protect rhododendrons, which tend to dry out. He said both methods have effectively reduced loss or damage.

Burlap wraps. A wrap of burlap or canvas can offer plants protection from desiccation and drift from deicing salts applied to driveways and streets. The recommended technique is to wrap the "bodies" of the evergreens without covering the top because some light is still needed during winter for growth.

Still, Rodie has observed that the jury’s out on wraps. "Burlap helps protect bark when trees are transplanted," he said. "But if you’re trying to prevent sun scald, you may get a lot of heat gain on the bark on the southwest side of a property and, at night, the air gets real cold. If you get enough warmth in tissues, the bark will freeze and crack at night."

Some people like to wrap the trunks of shade trees, but research is unclear as to whether that helps, he said.

Some contractors, he said, make the mistake of leaving burlap on year round. "Some trees have the capability to conduct photosynthesis in their bark," he said. "If you take a small tree and wrap it, they have less opportunity to produce food for themselves."

Other tasks. Sometimes Skelton uses a "winterizer," or a low-nitrogen fertilizer, to feed roots during winter months. "We have to be careful with that so that we do not put too much down to promote growth," he said.

Rodie warned not to fertilize too late in the season. "If a high-nitrogen fertilizer is put on in a warm fall, you get a lot of extra plant growth late in the year," he said. "This is not good because the growth won’t harden off in time and the plant can get a lot of freezing death or dieback."

Perennials or annuals generally don’t need much special attention, but some caution not to plant them too late. Smaller plants that haven’t had a chance to root properly may frost heave, Lowell said.

Rodie advises planting perennials in the Midwest before early September. "If you can’t plant perennials by early September, you risk not getting them established before the weather gets too cold," he said.

In warmer regions, winter preparations are often limited. Andee Bechtold, president, Longhorn Maintenance, Allen, Texas, said taking steps to protect plants can be more damaging than not protecting them. "Our sun can be hot enough to suffocate the plant under the protection we use from the cold," she said.

For successful overwintering in any area, plants must be cared for properly all year, Rodie said. "Overwintering is about how the plant is planted and year-round maintenance more than anything else," he said.