Valley Gardens: Beware the burning bush -- Non-native invasive plants are threat to habitats

By Cheryl Wilson

Published on April 06, 2007

Our yard is infested with invasive plants and my goal this year is to eradicate them. It won't be easy.

What exactly is the problem with non-native invasives? Basically, they take over the habitats of native species, plants that are relatively disease- and pest-free, plants that nourish birds and beneficial wildlife. The invasives usually are so vigorous and so prolific in their seeding that they prevent more fragile species from surviving. You might compare it to the fight over nesting boxes between native bluebirds and imported English sparrows.

"Anybody who spends any time outdoors and pays attention to what's growing has noticed we are under siege from damaging and dangerous invasive plants," said Allison Bell, a Northampton graphic artist and wildflower photographer. Bell is a volunteer for the Invasive Plant Atlas of New England, a federally-funded project to inventory the extent of invasive plants.

Trees like Norway maple are crowding out our gorgeous native sugar maples. Shrubs like burning bush and barberry are usurping the place of native viburnums in our woodlands. Purple loosestrife is taking over wetlands at the expense of certain bird species, as well as native vegetation. Water chestnut is clogging our streams and ponds.

"We are not concerned about 'thugs' in the garden," said William Brumback, conservation director for the New England Wild Flower Society, referring to plants like Silver King artemesia and Anemone sylvestris. "What we are really concerned about is plants that have escaped."

Many of the problem plants came from the gardens of well-meaning home horticulturists who simply wanted "something different" in their landscapes. That is why gardeners like me -- and you -- need to get informed about invasive plants, and start grubbing out the bad guys.

For the past decade environmentalists have been pushing state and federal authorities and the nursery industry to curtail sales of certain non-native invasive plants that are taking over native species in forests, fields and wetlands across the country. Massachusetts is actually a national leader in the campaign.

The Massachusetts Invasive Plant Advisory Group identified 66 problem plants that need to be controlled. Garden clubs and civic organizations planning plant sales this spring should obtain a copy of "A Guide to Invasive Plants in Massachusetts," which is available for a $2 shipping fee from the New England Wild Flower Society (www.newfs.com). This 80-page booklet has color pictures and descriptions of the problem invasive plants.

Sales of some plants, like autumn olive and Oriental bittersweet, are already banned. Others may be sold until January 2009 to give nurseries a chance to deplete their stocks.

South Amherst problems

Many of the invasive plants on our land grew from seeds scattered by birds. Multiflora rose, autumn olive and honeysuckles as well as Oriental bittersweet were certainly never on my planting lists.

Although we dug out the foundation plantings of barberry 30 years ago, we left one large specimen simply because I once saw a pheasant nibbling on its berries. Of course, the handsome bird never came again. That single barberry has spawned several babies now thriving in the middle of my favorite lilac.

I confess we did plant a burning bush (Euonymus alatus), which has produced an unholy number of seedlings over the years. Not long ago, an editor called me for advice. Should he plant a burning bush? "Don't!" I said.

"Don't?" he repeated.

"Don't you dare," I said.

I also admit planting certain problem perennial plants in my garden. About a decade ago I proudly grew dame's rocket (Hesperis matronalis) from seed obtained from the Royal Horticultural Society in England. It continues to thrive and I am loath to dig it up, but it is now illegal to sell it in Massachusetts. Another no-no is a charming buttercup I discovered in Newport and purchased at a local civic plant sale. It is Ranunculus ficaria or lesser celandine, also banned as of Jan. 1, 2006. Thank heavens I never was tempted by goutweed (Aegopodium podagraria), which is a huge problem along the Connecticut River.

Then there is the loosestrife along Plum Brook. When we moved here 30 years ago, there was just one large clump of Lythrum salicaria. Once we stopped mowing the wetlands along the brook, the loosestrife multiplied. The area was so bad it was even considered for an experimental release of a loosestrife-flower-eating beetle, but we didn't have a sufficiently horrendous situation. The loosestrife continues to multiply and the beavers have made the area so wet it is impossible to reach.

The New England Wild Flower Society has led the way in educating the public about the threat. It has collaborated with the Massachusetts Division of Fisheries & Wildlife, the U.S. Department of Fish and Wildlife and the Nature Conservancy in publications and conferences. Even the Massachusetts Nursery and Landscape Association has gotten involved by agreeing to a ban on selling certain invasive species.

The only way to eradicate most plants is to dig them out. A few, like the loosestrife, can be destroyed over time with biological controls like the flower-eating beetle.

The multiflora rose is a special problem in our yard. The huge old specimen below the barn is on the edge of a town swale leading to Plum Brook. We can't use herbicides to eradicate it. Also, it is a prime nesting area for cardinals and other songbirds. Brumback advised hiring a Bobcat bulldozer operator in late summer or early fall after the birds have finished nesting. In other areas, he said, Roundup herbicide could be effective. Perhaps we'll try that next to my beloved star magnolia, which was almost destroyed by the thorny arching branches of multiflora rose and twining bittersweet last year.

Planting alternatives

Once you have gotten rid of the offenders, the question is what to plant in their place. Fortunately, there are many possible choices. There is an excellent list in a new Conservation Notes issue, "Invaders...We're fighting back," published this spring by NEWFS. There is also an extensive list on their Web site.

Last year we planted a tupelo or sourgum (Nyssa sylvatica) in our backyard. We never had a Norway maple, thank goodness, but the tupelo is a great substitute if you need to get rid of that maple species that creates dense shade while providing little in fall color. We also planted an autumn-blooming clematis (C. virginiana) although we never had a vining honeysuckle.

Culver's root (Veronicastrum virginicum) is going to replace that dame's rocket and I'm adding Lobelia cardinalis to my stand of blue lobelia (L. siphilitica). See the sidebar for a list of the most important invasive plants in our area and a list of recommended substitutes.

The moral of the story is: Don't plant known invasives. Use native species instead.