Climate Change in the Garden

crape myrtle

There’s been lots of news lately about the effects of climate change on our gardens and oddly, it’s usually presented as good news to gardeners. They’re shown rejoicing over the warm-climate plants they can now grow, like crape myrtles in Upstate New York. BUT:

It's Global Weirding

Some plants are failing because the winter cooling period isn’t long enough. And others, like lilac, Eastern white pine, American arborvitae, Colorado blue spruce, and many junipers, suffer when summer evenings don’t cool down enough. Local garden writers are no longer recommending many of their old favorites for local gardens - like PJM rhododendrons and yews.

Rain events are more extreme, taking the form of longer droughts and more deluges. Not good for landscapes, for agriculture or for plants in our few remaining natural areas.

Longer warm periods mean more generations of some pests per year. Others, like the wooly adelgid that’s killing Canadian hemlocks throughout the East, are increasing their number because winters aren’t cold enough to keep them in check.

Weedy and noxious plants, like poison ivy, honeysuckle and kudzu, thrive in the presence of extra carbon dioxide, and poison ivy becomes more toxic than ever. Ragweed produces more pollen. Kudzu moves north. Some weeds, like Canadian thistle, are now resistant to herbicides.

Native plant populations are threatened by these changes in temperature, rainfall, pests and competitors, even the iconic ones chosen as state flowers and trees. In fact, the National Wildlife Federation predicts that 28 states will see their official plants become extinct by the end of the century. Picture Ohio without its buckeye or Kansas without its sunflower. Climate change has become a major threat to plant conservation, along with development and invasive species.

The East experienced a Miami-style January this year, followed by a frigid February. These alternating balmy+frigid periods take their toll on blossoms and whole plants. Fruit growers were particularly hard hit.

Hotter summers cause heat stress even to warm-season crops, like tomatoes, according to Cornell University.

More to Come?

The life cycles of insects, including the beneficial ones that keep others in check, may become out of synch with their prey. Pollinators, like the disappearing honeybees, may already be out of synch with the plants they feed on. Science Magazine reported in 2001 that earlier flowering and fruiting has caused such a disconnect for some long-distance migrating birds, who depend on food availability at the same time each year. And to make everything worse, most climate modelers predict more flooding and drought.

Even English Gardens are Adapting

To see how gardeners might adapt to all this change, let’s look first at what’s happening in England, a nation of gardeners. Last summer their southeast region had such a severe drought that sprinklers were banned. With more and longer droughts predicted, it’s clear that the very hallmarks of English gardening are now threatened - their traditional lawns and flower borders.

Thus the U.K. Environmental Minister is urging everyone to change their water usage, plant choice (look for drought- and heat-tolerance), and garden design - in other words, change everything they’re doing. No more roses and delphiniums. The use of gas-powered garden equipment is discouraged. Rain barrels are recommended, as are carbon-sequestering cover crops, like clover and winter rye. Brits are being given at least one bit of advise that fits their culture: plant roots are darn good at absorbing carbon dioxide, so plant more of them.

Changing Our Gardening Practices

Here in the U.S. we see the mainstream gardening media beginning to respond, with both Martha Stewart and Better Homes and Gardens advocating less gas mower and blower usage. Gardening authorities across the U.S. are offering these very good suggestions: add organic matter to make your soil hold moisture better, plant shade trees on the south side of your home to reduce air conditioning loads, and do your planting in fall or early spring. Even turfgrasses can be damaged by the freeze-and-thaw events we’re experiencing, especially where there’s standing water, so we’re being told to fix our drainage problems.

Choosing Different Plants

Research has really just begun, but here are the kinds of plants being recommended by gardening experts in response to global climate change:

Perennials from Mediterranean climates, which thrive without summer rain. Examples are such beautiful and useful plants as lavender, rosemary, sage, catmint, oregano, and thyme. The herb agastache flowers nonstop through the summer and is beloved by bees, and red agastache is a magnet for hummingbirds. Locally native plants are particularly good for sustaining wildlife, but be sure to ask for ones that will survive the new climatic conditions.

Choose trees and shrubs that do well across many temperature zones. Some have seeds that can shift strategies quickly, rather than the generations it usually takes for most trees to adapt to new conditions, which makes them so vulnerable to climate change. Oakleaf hydrangea, serviceberries, deciduous magnolias and many pines are especially adaptable to a range of conditions. Again, the science is evolving, with experts at Cornell currently saying they haven’t yet seen changes that cause long-term damage to trees and shrubs.

How Gardeners Can Help Reduce Climate Change

To borrow from one of the central tenets of organic gardening, the first goal of gardening should be to do not harm. Here are some ways:

Stop using gas-powered lawn equipment or products that use fossil fuels in their production, like synthetic fertilizers. Gas mowers spew as much pollution in one hour as a new car does in 40 hours - that’s how terrible the gas-mower technology is. And those synthetic fertilizers can be replaced primarily by compost and organic mulches, supplemented with organic, slow-release fertilizers when an extra boost is needed.

Instead of blowing leaves into plastic bags for them to be trucked away to landfills or to an incinerator, turn them into soil, by composting. Home compost operations help lighten pressure on landfills and result in more water-retentive soil for the gardener - that really cool circle of life thing. Some municipalities collect leaves and turn them into free leafmold mulch or compost.

Grow your own food. It’s fresh, it’s as organic as you want it to be, and it doesn't have to be trucked or flown in from far away. In the alternative, frequent our local farmer’s markets.

Finally, the quaint suggestion that we bring back a garden ornament from our grandmothers’ gardens - the clothes line - comes from the Goracle himself.

Zone Maps - a HOT Issue

The last time the U.S. Department of Agriculture amended its famous map of zones (bands of land that share the same winter low temperature), was 1990 and a promised update has been delayed. One wonders why. Is it because, as a spokesperson said recently on EarthBeat Radio, the mappers are in Iraq with their tours extended indefinitely? Many suspect another reason - that the Bush administration is trying to avoid documenting more proof of global warming. It didn’t help that the USDA rejected the map update done for them by the American Horticulture Society, and their explanations have been less than convincing.

Fortunately, someone stepped in to fill the void. The National Arbor Day Foundation recently released its own updated map, which shows many places a full zone warmer than in1990, which means their low temperatures are now 10 degrees warmer.

Article originally published in Maryland's Voice Newspapers. If you have any comments about this article, send 'em along.