It's human nature to look for a silver lining, and if there is one place where our warming climate isn't all bad news, it might be our own backyards. The latest climate studies show that the growing season has stretched by eight days and that northeastern winters are an average 4.4 degrees warmer than they were 30 years ago.

If you check out the new Arbor Day Foundation hardiness zone map, your garden might have moved a full zone or even two zones closer to the tropics. This means that it could be the right time to indulge that yen for camellias, plant that fig tree, or grow lettuce into November, provided you go about it in the right way.

With extra carbon dioxide (CO2) in the air, "plants are generally getting stronger, and growing faster," says Dave Wolfe, professor of plant ecology at Cornell University. But don't expect to spend more time in your hammock sipping lemonade. As the climate shifts, gardening is becoming more interesting but significantly more challenging.

Weeds
For one thing, weeds, including ragweed and poison ivy, are able to use that CO2 about three times as efficiently as your desirable plants. Why? Essentially, because they grow faster, says Wolfe. Not only that, but recent USDA studies show that weed killer becomes less and less effective as the temperature warms.

Get out of your hammock to:

• Pull those weeds.
• Give your plants everything they need; pay extra attention to soil preparation by adding organic material in the way of compost or manure.

Pests
Another unwelcome addition may be new pests, says Peter Del Tredici, senior research scientist at Harvard's Arnold Arboretum. "The hemlock woolly adelgid used to be killed off during the cold New England winters," he says. As winters are warming, this insect is creeping farther and farther north through eastern forests, wiping out the hemlock as it goes.

Other insects that might previously have met their end in the mouth of another insect may now live to dine on your vegetables and flowers. That's because a change in bloom time of a mere four days can throw an ecosystem into confusion. Life cycles of beneficial insects can swing out of sync with the bugs they help control, says Wolfe. The intricate relationships among species are too complex to allow us to predict exactly how plants will be affected by these changes.

Get out of your hammock to:

• Choose plants that are pest- and disease-resistant.
• Count degree days (which are increasing with global warming) to determine when to expect the worst pests in your garden.

Precipitation
Then there is the all-important question of rain. "Statistics tell us that we aren't experiencing less rain, necessarily," says Del Tredici. "But we're getting fewer and fewer rain events." That means longer periods of dry weather, which can kill off root systems and otherwise weaken your plants, punctuated by fewer heavy downfalls, which can drown or topple the enfeebled plants.

Get out of your hammock to:

• Select plants that generally require less water.
• Irrigate regularly by drip or other method to stabilize plants.
• Ensure good drainage to help plants survive torrential rains.

Fewer days of snow on the ground also means more stress for plants. Snow cover acts like a mulch to protect beneficial soil microbes and to protect roots from alternate freezes and thaws that can literally heave your perennials out of the ground. Icy winds on unprotected soil can cause the ground to freeze up to a foot deep or more, which can damage dormant roots.

Get out of your hammock to:

• Lay down mulch right after the ground freezes and leave it there till spring.

Soil
Aside from contributing to the overall rise in temperature, the burning of fossil fuels is also causing our soil to acidify. You may not see your backyard trees dying from the top down, says Del Tredici, but it's very likely that your patch of dirt is moving further away from the neutral pH that most plants like.

Get out of your hammock to:

• Check soil pH regularly and apply limestone where needed.

Climate projections show that, no matter what, we are on our way to a warmer world. If we don't cut back on emissions, parts of New York, Connecticut, and New Jersey will have the climate of Georgia within 70 years. We can take steps to adapt in order to tolerate the unavoidable. What can we do to avoid the intolerable?

For us as gardeners and lawn owners, there are key areas where we can slow things down.

• The first is to cut down on fertilizer. "For each ton of nitrogen fertilizer with ammonium sulfate or ammonium, four to seven tons of fossil fuels are burned," says Wolfe. Use compost or manure-organic sources of nitrogen without the high emissions cost. If that isn't practical, choose urea-based fertilizers over those with ammonium sulfate or ammonium nitrate. And with all fertilizers, use only the minimum amount required. As nitrogen fertilizer breaks down, it emits nitrous oxide (N20), the third most potent greenhouse gas.
• Next, swap the tractor mower for an energy-efficient push mower, a rechargeable mower, or, if your yard is small, one of the sleek, new lightweight reel mowers.
• Remember that while the mercury is generally rising, we can still get cold snaps, late snows, and even record-breaking chills. So if you do go in for camellias, buy just one first and wait a few years to watch and see how it does.

As Mark Twain famously put it, "Climate is what we expect, weather is what we get." As most gardeners know, that remains truer than ever.


Where to learn more

BUGS: This membership group for urban organic gardeners and landscapers offers advice info, soil testing, etc.

Northeast Organic Farming Association's organic land-care program: Includes sources for organic landscaping services

Climate and Farming: Studies and information relating to climate change, farming, and gardening

Heat zone map from the American Horticultural Society

National Wildlife Federaton's Gardeners Guide (PDF): What gardeners can do to help mitigate climate change

The New York Botanical Garden plans to hold an ongoing series of seminars on gardening and climate change

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