Creeper, American bittersweet alternatives to invasive species

Last week’s column on Oriental bittersweet, Celastrus orbiculatus, prompted several readers to inquire about native alternatives to this non-native invasive vine. Other readers wanted to learn about alternatives to burning bush, Euonymus alatus, and Japanese barberry, Berberis thunbergii, two more invasive species still firmly entrenched in commercial horticulture.

Here are some suggestions.

Two native alternatives to Oriental bittersweet come to mind. American bittersweet, C. scandens, a close relative of the Asian species, inhabits open woods, woodland borders, shrub thickets and fencerows throughout New England. In some areas, however, populations of the native bittersweet have been severely overrun by the more aggressive invasive species and hybridization between the two species has further contributed to the decline of the native species. Although I often botanize in areas of Maine where American bittersweet once grew, I have yet to see a single plant.

I will know it when I see it, if it is in fruit. The red-orange fruits of American bittersweet are twice the size of the Asian species’ and are carried in dense clusters at the tips of the branches. Oriental bittersweet’s fruit clusters are found along the stems in the leaf axils.

While not as rampant as the invasive species, American bittersweet is a vigorous vine that will grow to 20 feet or more if not pruned. The long twining stems are covered with broad oval leaves that turn clear yellow in autumn before dropping, leaving colorful fruits to adorn trellis or wall.

Gardeners may buy plants of American bittersweet, primarily through mail-order nurseries. It is important to buy both male and female vines to ensure pollination and fruit set. Also, there have been reports of American bittersweet plants turning out to be hybrid seedlings, so buyers beware.

Virginia creeper, Parthenocissus quinquifolia, is another native vine worthy of consideration as an alternative to Oriental bittersweet. Use it to cover a fence or arbor with fiery-red foliage in autumn and indigo berries covered with snow in early winter. The berries also make Virginia creeper one of the most valuable plants in the bird garden.

Burning bush and Japanese barberry, two non-native invasive shrubs with similar rounded growth habits, are grown primarily for their colorful fall foliage. I recommend highbush blueberry, Vaccinium corymbosum, as an alternative for both. With autumn leaves of dark red and plum mixed with yellow, white bell-shaped spring flowers, and edible fruits, highbush blueberry is truly an all-season garden shrub.

Of course, no gardener in her right mind would consider turning the upright broad-spreading form of highbush blueberry into meatballs, cubes and pyramids, as is so often done with burning bush. In this sense, there is no alternative, nor need there be.

Black chokeberry, Aronia melanocarpa, comes to mind as a splendid alternative for burning bush. White flowers with pink anthers open in midspring among shiny dark green leaves, followed by glossy black fruits that persist from late summer into winter. The dark fruits provide striking contrast to the crimson fall foliage.

Many Maine natural areas are rapidly becoming monocultures of Japanese barberry and this will stop only when this invasive species is removed from landscapes and nurseries. It can be replaced by a variety of native shrubs, including diervilla, Diervilla lonicera, often sold as Northern bush honeysuckle, a true misnomer since it is not a true honeysuckle and not related to the non-native invasive shrub honeysuckles. We grow diervilla in Marjorie’s garden, delighting in the bronze-tipped new foliage in spring, the clusters of yellow flowers that entertain bumblebees throughout the summer, and the mix of clear yellow, apricot and scarlet fall foliage.

Gardeners have choices. There are numerous native alternatives to the invasive plants that threaten the diversity and beauty of Maine’s natural areas.

Send queries to Gardening Questions, P.O. Box 418, Ellsworth 04605, or to rmanley@shead.org. Include name, address and telephone number.