How native are your native plants?
Many virtues are claimed for native plants: They can handle the local climate, are drought-tolerant (at least if they come from the prairie) and require less maintenance (if you choose the right native plant for your garden's conditions). And native plants provide food and shelter for native wildlife.
But if you buy a pot of coneflower, tickseed, little bluestem grass or smooth hydrangea from a garden center or catalog, it's probably not exactly the species that grew here centuries ago. It's more likely to be a cultivar, or cultivated variety, selected for some characteristic that makes it more attractive or useful and easy to sell to gardeners.
Sometimes the change comes from the normal variation that occurs in every generation of plants. In other cultivars, it was deliberately sought by careful crossbreeding, even between different species. Sometimes cultivars of native plants are referred to as "nativars."
A cultivar may have more conspicuous blooms, like Annabelle hydrangea (Hydrangea arborescens 'Annabelle'), which has much larger fluffy white flower clusters than the native smooth hydrangeas. It may be more compact, like Kim's Knee High coneflower (Echinacea purpurea 'Kim's Knee High'). It may bloom longer or at a different time than the native plant, or it may be less susceptible to diseases and insects. It may have a leaf color or bloom shape not found in nature, like coneflowers and coreopsis with flowers that are double or downright odd.
In the form of cultivars, many native plants — or sort-of native plants — have been welcomed into the mainstream of gardening. But there's a question: Do they really work like native plants? Do they still serve the functions of native species, particularly in supporting animals?
For many enthusiasts, that's the most important reason to use them: To provide habitat for a wide variety of other species.
The manifesto of these gardeners is "Bringing Nature Home: How You Can Sustain Wildlife with Native Plants" by University of Delaware entomologist Douglas Tallamy (Timber Press, 360 pages, $19.95; bringingnaturehome.net). And cultivars worry Tallamy because he fears that altering native plants to make them more attractive to people may make them less useful to animals.
If the plant blooms earlier or later in the year than the original species, will it still be in sync with the life cycles of the insects that pollinate it? If the leaves are purple instead of the regular green, has the chemistry changed enough to turn off insects that use it as a food source?
Hello Yellow butterfly weed (Asclepias tuberosa 'Hello Yellow'), with bright yellow flowers instead of the normal orange, appeals to Peggy Anne Montgomery, publicist for American Beauty Native Plants, a partnership with the National Wildlife Federation that markets cultivars as well as straight species.
"I think it's kind of fun to have another color," she says. "And the insects don't care."
The problem, though, is that we don't really know whether the insects care or not. "Nobody has studied this in a scientific way," Tallamy says. The first attempts to answer the question are just beginning.
Other advantages claimed for native plant cultivars that matter to gardeners — drought-tolerance, hardiness, low maintenance — can be tested in the marketplace. But only careful scientific study can hope to discover whether cultivar differences matter to birds, insects and microorganisms.
Such research has started at the University of Vermont, where doctoral candidate Annie White is studying whether insects such as native bees that gather pollen and carry it from bloom to bloom will visit cultivars as often as they visit the straight species.
In her first year's data with a small number of plants — hardly enough to settle the question — the results were suggestive: Six of nine native species attracted more native pollinators than the cultivars she planted with them. The light purple flowers of the straight native species New England aster (Symphyotrichum novae-angliae), for example, got more than a dozen times as many visits as the popular cultivar Alma Poetschke (Symphyotrichum novae-angliae 'Alma Poetschke'), whose blooms are vivid magenta.
On the other hand, the bees were equally happy to visit either cultivars or straight species of wild bergamot (Monarda fistulosa) and giant hyssop (Agastache foeniculum).
White's guess, she says, is that "real ecological trade-offs" come in when the plant is very different form the straight species, with a distinctively different color or flower form.
For most gardeners, the debate over cultivars and natives is almost moot, because only cultivars are available. True native plants are difficult to find in garden centers.
Natural Garden Natives, a line of native plant species from locally collected seed, finds a market largely through plant groups' spring sales. "There's a two-week window in May when you can find them," says Trish Beckjord, who specializes in native plants at the wholesale grower Midwest Groundcovers in St. Charles, Ill. Otherwise, you must persuade your local garden center to order them.
Tallamy wishes gardeners would take that step. "I would like to see the homeowner say to the garden center, 'I would like to have the choice of a real native species,'" he says. "You can still have the cultivar."
Some say that cultivars have value, even to the cause of native species. "Cultivars can help the starting gardener or help someone make the transition to more native plants," Beckjord says.
Perhaps there is a range of native-ness in which every gardener can find a comfort zone. Tallamy and co-author Rick Darke have just published an inspirational book, "The Living Landscape: How to Design for Beauty and Biodiversity in the Home Garden" (Timber Press, 392 pages, $39.95), to help gardeners create attractive and accessible habitat gardens.
In smaller or less casual gardens where big plants won't fit, perhaps lower, tidier native species might find a place among the foreign-born peonies and day lilies.
A short coneflower may still feed a goldfinch in a tiny garden where its tall ancestors would flop. And it may be the first plant to connect a 21st-century gardener to the prairie past.
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