With record warmth throughout the Northeast in December and early January, gardeners and commercial growers are asking: "Will the warm weather wither my plants?"
The quick answer is: It depends. But expect fewer blooms on flowering trees and shrubs in the spring.
In addition to the particular plants involved and your location, how your plants fare depends on how quickly the cold temperatures returned, how cold it gets, and other environmental factors.
"I don't think we've seen the extremes yet that would cause a lot of long-term damage to trees and shrubs," says George Good, Cornell professor of horticulture and a landscape plant expert.
A sudden drop to subzero temperatures following the warm weather in early January would have severely stressed many plants, says Good. But most plants should acclimate well since the return to more-normal winter temperatures experienced in much of the Northeast has been gradual.
"Some flower buds will be killed. So we may see fewer blooms on flowering trees and shrubs this spring," predicts Good. That has commercial fruit growers concerned, as they will harvest less fruit if too many flower buds die. But for most of us, it just means we'll see fewer flowers.
To reduce potential problems, Cornell horticulturists suggest the following:
Lawns: Although the unseasonable warmth encouraged root growth and young seedlings, if temperatures drop too fast, lush top-growth may be more prone to freezing damage. So, avoid walking on lawns as much as possible until the soil dries out and grass starts growing again in spring, says Cornell horticulturist Marty Petrovic.
If temperatures fluctuate a lot, it could kill grasses, says turf specialist Frank Rossi. Note low-lying areas where water collects and ice forms, and plan to improve drainage before next winter. Replant bare spots this spring before weeds have a chance to move in. For directions, see http://www.gardening.cornell.edu/lawn.
Trees and shrubs: A warm winter may prompt some ornamentals to flower prematurely, says Nina Bassuk, woody plant specialist and director of the Urban Horticulture Institute. "We'll lose some of those flowers for this season, but the long-term health of most [of these] plants probably won't be affected," she says.
Berries: If you mulched your strawberry patch, the plants should be fine, says berry specialist Marvin Pritts. Blueberries are slow to respond to warming temperatures, so he's not worried about them flowering prematurely. A rapid chill could freeze some of the blackberries and raspberry buds, but even if the entire cane dies, healthy new canes will emerge in spring; even if this summer's berry crop is lost, 2008's should be fine, says Pritts.
Perennial flowers: Most bulbs and perennial flowers should come through the winter just fine, says Bill Miller, director of Cornell's Flower Bulb Research Program, even if they started to flower. "The flowers that opened will probably survive, especially if we get some snow cover before really cold weather returns," says Miller.
It's common for the leaves of some bulbs, such as grape hyacinth and early daffodils, to emerge in fall or winter. The leaves may suffer some damage. But the flower buds are still deep underground and well protected from cold weather.
Vegetable gardens: The warm weather in December was great if cover crops or such cool-season greens as kale were planted, says Betsy Ingall, a technician who manages vegetable research plots at Cornell's Thompson Research Farm in Freeville, N.Y. But vegetable gardeners and commercial growers should be on the lookout this season for pests they may not have had to deal with following colder winters. When planning this year's vegetable plantings, consider testing some new pest- and disease-resistant varieties that also might perform better during hot seasons, she suggests.
Cornell horticulturist warns that warming trend could change what plants to grow -- and what pests will attack
In the future, chances are good we will see more warm winters like the one that, before early January, at least, had the Northeast basking in unseasonably high temperatures, says David Wolfe, Cornell professor of horticulture.
"We may still have some very cold winters," says Wolfe. "But all the climate models point to a warming trend, and nature is already responding to the warmer conditions."
Wolfe, who studies how climate change -- caused in part by increasing carbon dioxide levels in the atmosphere -- is affecting agriculture in the Northeast, says there is mounting evidence that the climate is warming. In the Northeast, he says, lilacs are blooming four days earlier on average than they did in the 1960s. Warmer temperatures are also affecting such cultivated crops as grapes (blooming six days earlier) and apples (blooming eight days earlier).
Studying long-term climate trends can't pinpoint what the weather will be like next week or next winter. But Wolfe says that warmer winters could allow gardeners to grow some plants that previously could only grow in milder climes. And the wine-grape industry, which relies on varieties that are only marginally cold-hardy in upstate New York, may benefit from warmer winters.
On the other hand, aggressive weeds and invasive plants would also move north. Studies show those species are better equipped than crops to take advantage of the increasing carbon dioxide levels in the atmosphere that are driving warming, notes Wolfe.
Pests and diseases that were held in check by the cold could become more of a problem. Life cycles of beneficial insects might get out of sync with the pests they help control.
Natural ecosystems would shift north, with oak-pine forests replacing maple-beech-birch forests in some places, for example, Wolfe notes.
Less reliable winter snow cover could hurt overwintering of some perennial crops and flowers, and hotter summers would cause heat stress even in such warm-season crops as tomatoes.
It's uncertain, says Wolfe, if weather would become more variable along with higher temperatures. Most models, he observed, predict fewer but more concentrated precipitation events, causing more flooding and drought.
For gardeners, adapting to a changing climate may be as simple finding better-adapted tomato varieties or other plants to grow. But for commercial growers, changes would likely be more involved. "Everyone is going to have to invest some to respond to climate changes," says Wolfe.
For more information, see "Climate Change and Northeast Agriculture" at http://www.climateandfarming.org.
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