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The Greenhouse EffectGlobal warming's impact on your garden.

By Constance Casey
Posted Wednesday, Feb. 28, 2007, at 12:20 PM ET

(Continued from page 1)

A less obvious effect of making and using compost is to keep the atmosphere healthier. When the stuff rots in a municipal landfill, instead of decomposing in a nicely aerated compost heap, it exudes methane—a greenhouse gas that traps heat on Earth at a greater rate than carbon dioxide does.

Selecting plants for drought tolerance doesn't mean that your yard will be all yucca and cactus. Lots of favorite annuals bloom well with low water—cosmos, petunias, verbena, marigolds, and zinnias. (Remember that even drought-tolerant plants need to be watered thoroughly when they're first planted.)

Perennials from Mediterranean climates have evolved to thrive without summer rain. Pinch the leaf of a plant native to Provence or Greece (and similar climates in coastal California, South Africa, and Chile), and you'll see these plants are resinous and fragrant. These include useful and beautiful plants like lavender, rosemary, sage, catmint, oregano, and thyme. A less familiar herb—agastache, also known as hyssop—is a real garden star; it flowers nonstop through the summer, beloved by bees. The red agastaches attract hummingbirds.

The Denver Botanic Garden, which has long been landscaping with natives adapted to Colorado's semi-arid climate, has clear advice and useful plant lists. The catalog of High Country Gardens in Santa Fe, N.M., has particularly interesting water-smart planting designs including "The Inferno Strip Garden"—for hot, narrow spaces.

Any botanical garden will have good advice on the native plants that can stand up to hot summers; planting natives will make life easier for your local birds and beneficial insects.

Like everything involved with interacting with the natural world, water-wise gardening gets a little complicated. Climate watchers who are warning us of longer droughts also are predicting heavier rains in winter, coming in fewer events—downpours, buckets. The plants from the Mediterranean or the Colorado high plains do not do well if their roots are drowned. Happily, and also paradoxically, a good cure for waterlogged soil is to add organic material. It's an apparent paradox because that's the stuff that holds on to water, but the organic stuff also keeps the soil aerated and keeps water from collecting in fatal puddles.

You can hedge your bets in this chancy new world by choosing trees and shrubs that do well across many temperature zones. Among the most adaptable: oakleaf hydrangeas, amelanchiers, many of the deciduous magnolias, and a lot of the pines. It may not be precisely right, I suddenly realize, to use the word adaptable. People are adaptable; we can change our behavior. (Not long ago no one used car seatbelts, and everybody smoked.)

It's more accurate to say that some plants and trees have evolved to tolerate or survive or withstand a range of conditions. There are some clever little weeds that can shift strategies quickly, but for the most part it takes generations for trees to adapt to new conditions, which makes them terribly vulnerable.

The tree losers in the coming warming, sadly, are sugar maples and white birches, which thrive in a niche and are unwilling to adapt. Their populations are dwindling in the warming Northeast, land of the precocious lilacs.

Gardeners tend to be the most adaptable of human beings. In fact, working in a garden is an experience that trains you to be flexible and to find consolations where you can. So the poppies never came up and deer ate the roses? Well, the irises looked great, and the lilacs were fabulous.

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Constance Casey, a former newspaper editor, was a New York City Department of Parks gardener for five years. E-mail gardening questions to .
Photographs of: the hardly-any-water-at-all garden by Scott Dressel-Martin, the Denver Botanic Gardens; the sun on Slate's home page by Digital Vision/Getty Images.
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Remarks from the Fray:

Everyone but the right wing* nutcases and the people who listen to them on the radio has no choice but to admit that global weather patterns, data in trees and ice, and physical evidence from the arctic to central Africa point towards gloabal warming.

However, however, however-- I think it's a bit premature to start ripping out trees and planting cacti. As trees and shrubs and flowers die off, when replacing them people might want to think of shifting to a plant that is more heat tolerant, more drought resistant and so on. But within the framework of general weather patterns, there are other cycles and phenomena that affect weather at a local level for a short time. The jetstream, for example, shifting a wee bit north, has given us here in New England considerably milder than usual winters recently. Even if global warming is present, if that jetstream bends lower next winter, it will be colder here. It's way too soon to be thinking about planting trees that can't handle -20F here. Three years ago we had a cold snap that felled many trees, killed shrubs and plants, and caused pipes to freeze that had been fine for the prior 60 years.

Many plants can live within a range of climate. This means that most trees and flowers will be fine over the short term, and that only over much longer periods will we see a march northward of the Zones. If Krakatoa were to erupt again (which isn't possible) and dump thousands of cubic miles of stuff into the atmosphere, then we would see a short term effect very quickly. But what we seem to be near is the threshold of a change in long term weather patterns, and that's an entirely different cup of manure tea...

--MRHULOT2

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The article on gardening and global warming seems to ignore the other side of the climate change coin. I have read a few places that climate is expected to get more extreme in general - hotter summers, yes, but also colder winters. In NJ, we've had record setting cold snaps this year. Last year was brutally cold as well. And the wind has been wicked this winter.

That severe cold and strong, dessicating wind takes a serious toll on tender plants. I don't know if my three little roses will still be alive come spring. They're on a southwestern wall, fully exposed to the westerly winter winds. (Don't blame me! The previous owner planted them!). It certainly hasn't been a mild, warmer winter this year, and anyone who planted less cold-hardy perennials and shrubs round here is probably regretting their choices. I wouldn't start shifting my choices to Zone 7 plants until I see quite a few years of Zone 7 winters. For now, I'm looking for plants with a wider hardiness range, and expecting to have to baby them through their first tough summers and winters.

--tilia

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