Global Climate Change, sparking a change in the USDA Garden Map

Every gardener is familiar with the multicolor U.S. map of climate zones on the back of seed packets. It's the Department of Agriculture's indicator of whether a flower, bush or tree will survive the winters in a given region.

It's also 18 years old. A growing number of meteorologists and horticulturists say that because of the warming climate, the 1990 map doesn't reflect a trend that home gardeners have noticed for more than a decade: a gradual shift northward of growing zones for many plants.

The map doesn't show, for example, that the southern magnolia, once limited largely to growing zones from Florida to Virginia, now can thrive as far north as Pennsylvania. Or that kiwis, long hardy only as far north as Oklahoma, now might give fruit in St. Louis.

Such shifts have put the USDA's map at the center of a new chapter in the debate over how government should respond to climate changes that were described in a report last year by a United Nations-backed panel of scientists. The panel said there was "unequivocal" evidence of global warming fueled by carbon dioxide emissions, which have created an excess of the greenhouse gases that help keep the Earth warm.

Climate change is boosting interest in energy-saving hybrid cars and compact fluorescent light bulbs — and reshaping how people garden. Across the agricultural industry, the subject is driving a dispute over climate maps that involves economics, politics and meteorological standards.

At nurseries across the nation, it has become common knowledge that the government's climate map is out of date. And yet the nursery industry, which had $16.9 billion in wholesale sales in 2006, has joined the USDA in taking a conservative approach to changing the map.

So what does this mean to Rochester? Should the region be placed in a different zone? Can we now grow plants seen in states south of us?

Well, the answer is yes and no, according to local horticulturalists and landscapers. They say gardeners should definitely still count on Memorial Day as a plant date even if the weather seems warmer earlier.

Generally, the lower the zone number, the colder the region. The Rochester region is generally zone 5. Because of the effects of Lake Ontario, however, there have always been wide swings in the region, with some properties near the lake in zone 6, or even zone 7, while the higher elevations south of Rochester dip into zone 4, says Walter Nelson, horticulture program leader for Cornell Cooperative Extension in Monroe and Ontario counties.

Nelson says the changes, even locally, are being widely debated.

"The sum game: Area gardeners are growing plants they might not have been able to grow in years past, (but) if we get a cold snap at the wrong time, that (will be) a reality check," Nelson says.

Bruce Zaretsky, a landscape designer and president of Zaretsky and Associates in Penfield, agrees that some people have grown plants that couldn't be grown in Rochester a few decades ago. For example, a Webster client grew a camellia, which Zaretsky hadn't seen north of Long Island.

However, what is happening is that borderline zone 5 plants such as rhodys, hydrangeas and dogwoods are blooming longer and are flowering better because the area isn't seeing as many low-temperature mornings that would freeze the buds off, he says.

"It seems to me that our winter climate has mellowed in the 22 years I've been up here," he says, allowing people to experiment with more flowers. They just have to take care to protect the plants if the weather changes.

Christine Froehlich, executive director of the Rochester Civic Garden Center and a resident of Sodus Point, Wayne County, is a relative newcomer to the area, having moved here five years ago. What she sees as a bigger issue than temperature is the unpredictability of weather systems.

"It does seem to me that it's gotten a bit warmer," she says. "But it seems like we have more variability than we used to have. As a gardener, you definitely can't count on things the way we used to. It seems we have more severe weather changes — severe drought, severe rain."

Whether Rochester is zone 5 or zone 6 might not matter much to the average gardener who might like to experiment with different plants anyway.

But it's a key issue for commercial growers, worried that their losses won't be sufficiently covered by the Federal Crop Insurance Corp.'s Nursery Crop Insurance Program, which covers them for losses caused by weather-related events such as flooding. If growing zones move north because it's warmer, there's still a possibility of cold snaps, and it's unclear exactly how nursery insurance programs would deal with that risk.

And analysts say many in the nursery industry nationwide are worried that adjusting the climate maps would encourage customers in cooler areas to buy tender, warm-weather plants that would be unlikely to survive a cold snap. That could cost them money because many businesses offer money-back guarantees on plants.

The nation's climate zone map designates 11 major belts for growing plants, from the relative cold of zone 1 — which includes Fairbanks, Alaska — to mid-range temperatures of zone 6 (which includes parts of Missouri, Tennessee and southern Pennsylvania) to the heat of zones 10 and 11, which include Hawaii and southern Florida.

Changing boundaries for various zones to reflect recent warming could "have a significant impact on certain growers of certain plant species," says Dave Hall of National Crop Insurance Services, an organization that represents crop insurance companies.

Economic factors shouldn't be placed above the science of climate change, says meteorologist Mark Kramer, who lives in Westchester County, who worked on the 1990 USDA map that remains in effect, as well as a proposed update in 2003 that showed a warming trend. The USDA rejected the 2003 map.

"If nature changes, industry should change with it," Kramer says. "If the weather changes, we shouldn't operate with zones and systems that aren't appropriate."

USDA officials reject suggestions that the agency's resistance to changing the 1990 map reflects a reluctance to acknowledge the potential impact of climate change.

The agency's delay in releasing an updated map has led another group to release its own climate map. In 2006, the Arbor Day Foundation put out a map based on data from 1991 to 2005 that shows a significant northward movement of warm zones for plants and crops.

"Everyone's entitled to their opinion," says Woodrow Nelson of the Arbor Day Foundation of the USDA map. But he says his group, which provides low-cost trees, was seeing trends that it wanted reflected in a map for growers.

"Flowering dogwoods and southern magnolias and even crape myrtles that are so popular in the South are now having great success all the way up into Pennsylvania and even up into Michigan," Nelson says. "Douglas firs and Colorado blue spruce, which were historically mountain trees, are becoming a very popular landscape tree in the Midwest. With the millions of trees that we're putting into the hands of people across the country, the most recent data available is important. Data from 30, 40 years ago is really kind of irrelevant in the life of a young tree."