By Sarah Robertson
Garden columnist | Posted: Sunday, May 3, 2009 12:00 am
As I knelt alongside a section of rock wall last weekend, shovel in hand, I paused momentarily to fully appreciate the view: roots from a seemingly benign plant running for more than two feet beneath its neighbors, strangling everything in sight.
Strong roots. Tenacious roots. Roots that entrench themselves in fifteen nearby desirable plants, thereby making eradication almost impossible.
We've been fighting this perennial menace - a virulent strain of Campanula poscharskyana - for two years, ever since a large Douglas fir came down and brought more sunlight into a formerly shaded corner of our front garden.
Brighter conditions transformed a mildly thuggish plant into the Incredible Hulk of perennials, and prompted a fair bit of panic on our parts as we watched the bellflower attempting to choke out, well, everything.
Thanks to regular stints of grubbing this plant down to the roots, it no longer has a stranglehold on our front garden. But the potential is still there. We'll need to remain ever-vigilant in our efforts to vanquish this bellflower from our landscape.
Plants with an aggressive, take-over-the-world mentality are termed invasive, and have the potential to take over natural areas as well as landscapes. Many designated invasive species are already spreading at an alarming rate.
Here in Oregon, the common Scotch broom costs our state an estimated $47 million annually in lost timber production alone, according to the Department of Agriculture.
Gardeners also purchase invasive plants, lured by their beauty and supposed low maintenance. Butterfly bush (Buddleia davidii), Russian olive (Elaeagnus angustifolia), English ivy (Hedera helix), purple loosestrife (Lythrum salicaria), yellow flag iris (Iris pseudacorus), English holly (Ilex aquifolium) and purple pampas grass (Cortaderia jubata) are just a few examples of popular invasives.
Dr. Sarah Reichard, head of conservation at the University of Washington Botanic Garden, researches invasive plant species and is also an avid gardener.
In the spring issue of The Savvy Gardener, an e-newsletter published by the Saving Water Partnership, a coalition of local water utilities in Seattle and surround King County, Wa., Reichard encourages gardeners to make thoughtful purchases as they make the rounds of nurseries and plant sales over the coming weeks.
She says that invasive species threaten not just favorite garden perennials, but a host of native species. Invasives can shift nutrient and water balances within the soil, or even poison nearby plants through exuded chemicals.
And, as most of us have discovered to our sorrow, invasives spread easily - especially from urban gardens, where excellent growing conditions make for exceptionally healthy interlopers.
Gardeners who live near natural areas have a special responsibility to garden carefully, says Reichard. It's very easy for seeds to be carried from one area to another by birds or the wind.
Even motor vehicles are surprisingly efficient seed movers. One botanist collected all the seeds and soil from his car for a year. The results? Some 3,926 plants - 124 distinct species - had hitchhiked on his car from all parts of the country.
Our goal, as responsible gardeners, is to prevent the introduction and spread of invasive species. To do this, it helps to be informed. A free, 54-page, full-color guide called "GardenSmart Oregon," is available from local extension service agencies and many area nurseries. You can also print out a downloadable PDF version through the Nature Conservancy of Oregon (www.nature.org/wherewework/northamerica/).
This terrific guide identifies more than 25 invasive plants that can easily escape gardens and threaten natural areas. There are crisp, clear color photos of the invasives, as well as excellent photos of noninvasive replacements appropriate to various regions of Oregon. Alternatives include both native and ornamental choices commonly available at local nurseries.
Here are a few additional guidelines to prevent the introduction and spread of invasive plants:
* Remove invasive species from your property. Replant with suitable replacements.
* Avoid buying plants with invasive tendencies. Such species may have words such as "vigorous," "spreading," and "fast-growing" included on their description.
* Be careful about trading plants with other gardeners if you know they have invasive plants growing nearby. Resist the urge to pot up those freebies - you may bring home a thug.
* Participate in work groups to remove invasive plant species under the guidance of knowledgeable professionals. * Participate in early warning systems by reporting invasive species in your area. Here in Oregon, a campaign called "Stop the Invasion" is working hard to spread the word to all parts of our state. Report invaders or noxious weeds by calling the Invasive Species Hotline at 1-866-INVADER, or by going online to www.oregoninvasiveshotline.org.
Finally, it helps to know what to do with invasive species once you find them. If they're out in the wild, make a report. If they're in your garden, remove and compost in your municipal green-waste cart or home compost bin. Just make sure the compost gets hot enough to kill any seeds.