Browse by title articles:

Resolve to Avoid These Invaders!

by Dr. Leonard Perry, Extension Professor,University of Vermont    

Gardeners love new plants! Over the years, thousands of plants "from away" have been introduced to our northern New England landscape. Many of these alien plants have become favorites: lily and peony in the perennial garden; crabapple and ginkgo in the landscape; and lilac and forsythia in the shrub border.

Occasionally, however, alien plants have become problems. Some have invaded our landscapes because they produce huge numbers of seeds that germinate well under many conditions. Others have aggressive root systems that crowd out native plants. Still others left their natural diseases and other problems behind, and do not have any enemies in this part of the world to keep them in check.

"Tame" non-native plants can be beautiful additions to the landscape. But avoid the invaders! Here are some plants that have become serious weed problems in northern New England:

Purple loosestrife (Lythrum salicaria) is the purple-flowered perennial that has come to dominate some of our wetlands in recent years. One mature purple loosestrife plant can produce over two million seeds in one season. This plant develops a sturdy root system, and even a small piece left in the ground can grow into a new plant. If you're looking for a substitute for this plant in your flower garden, try the gayfeathers (Liatris species).

Japanese barberry (Berberis thunbergii) has long been a popular landscape shrub, often used as a thorny barrier along property lines. But birds eat its orange-red fruits and disperse the seeds over long distances. When deer graze on understory plants, they often leave the thorny barberry seedlings, which then gain a foothold in an area and outcompete other plants.

Oriental bittersweet (Celastrus orbiculatus) has long been prized for its long, vining stems with colorful orange and red fruits, which are used in winter wreaths and arrangements. Unfortunately, this plant is very aggressive. It climbs and strangles woody plants in our forests and has displaced much of our native bittersweet.

Non-native honeysuckles (Lonicera species) produce juicy red or orange fruits that are eaten by birds. The seeds dispersed by this method germinate readily, and the new plants grow quickly to take the place of less aggressive plants.

Multiflora rose (Rosa multiflora) has long been used as the rootstock onto which hybrid roses are grafted. The aggressive multiflora roses often overgrow the top-grafted hybrids and then produce abundant flowers. The fruits contain many seeds. Birds and other animals disperse the plant. Multiflora rose is becoming a common site along our roadsides with its clusters of fragrant white flowers in early summer.

To help preserve the northern New England landscape:

• Select plants that do not escape from your garden.

• Grow more native species in your landscape.

• Urge local garden center and nursery managers to expand their selections of propagated native plants.

Eliminate invasive aliens from your landscape, taking care to remove entire root systems as well as top growth.

(Adapted from the North Country Garden Calendar)