In Rhode Island, invasive plants threaten native ecosystems as well as the economy. These introduced plants have few to no natural predators or diseases in Rhode Island to check their growth. Because of this, they spread aggressively, rapidly crowding out native plants that support local wildlife. Woodlands become impassable due to thick stands of nonnative undergrowth, and waterways become choked with mats of weeds. Some of these invasive plants in Rhode Island are still grown in gardens and readily available in nurseries!
But this threat is not insurmountable. As gardeners, we can start taking action in our own backyards. The first step, as with many things, is to learn. Learn about some of the worst and most common invasive plants in the state so you can recognize them when you see them. Then, you can take steps to remove any you find on your property. And this is the fun part: you get to replace the invasives with new plants (yay for plant shopping)! While any noninvasive plant will do, a native species will be well adapted to your growing conditions and support native wildlife like butterflies and birds.
Invasive Plants in Rhode Island
The following are some of the worst invasive plants in Rhode Island that you might find in your garden or for sale in nurseries and garden centers. If you recognize one on your property, check with your local Extension office for proper removal methods. And if you see any for sale, kindly inform the seller of the invasive nature of the plants and ask the seller to stop offering them. Each description in this list also includes suggestions for a couple similar native plants you can grow instead.
1. Norway maple (Acer platanoides)
Norway maple, a medium to large tree, grows up to 50 feet tall and casts dense shade with its broad crown. It also has a competitive, shallow root system that dries out the surrounding soil and produces chemicals toxic to many other plants. As a result, Norway maple can easily form homogenous stands with only its own seedlings surviving in its shade. Though its palmate leaves closely resemble those of the native sugar maple, breaking a petiole (leaf stem) of a Norway maple will release a milky sap not present in other maples.
In addition to sugar maple (A. saccharum), red maple (A. rubrum) also makes a lovely, very similar, native alternative to Norway maple.
2. Autumn olive (Elaeagnus umbellata)
A deciduous shrub, autumn olive has alternate, oval leaves with a pointed tip, dark green upper, and silver-green underside. Its brown stems have silvery speckles and long thorns. Small, fragrant, pale yellow flowers grow in clusters in the leaf axils and are followed by small berries that ripen to red with pale speckles in fall. This dense shrub can resprout from stump and root fragments and spread via the abundant berries, which are popular with birds, to form impenetrable stands.
Native elderberry (Sambucus canadensis) has a similar habit and produces masses of creamy flowers followed by berry clusters that birds love. For a suckering shrub suitable for large areas consider smooth sumac (Rhus glabra), which has attractive fall color and red berries.
3. Japanese barberry (Berberis thunbergii)
Another dense, stand-forming shrub, Japanese barberry has very small, oval to spatula-shaped leaves in shades of green, blue green, or deep purple. Its grooved stems have a sharp spine at each node and appear to have a slight zig-zag shape. In spring, umbrella-shaped clusters of pale yellow flowers bloom along each stem, replaced by crimson berries that ripen in late summer and persist into winter.
Eastern ninebark (Physocarpus opulifolius) also comes in a variety of leaf colors, and American cranberrybush viburnum (Viburnum trilobum) features showy white spring blooms, red berries, and beautiful fall foliage.
4. Privet (Ligustrum spp.)
Border, Chinese, European, and Japanese privet are all invasive, semi-evergreen to deciduous shrubs commonly used as hedges. These medium to large, multi-stemmed shrubs have small, dark green, ovate leaves in an opposite arrangement. Clusters of white flowers appear in summer and give off an unpleasant fragrance. The glossy, blue-black berries that follow often cling to the plant through winter.
Bayberry (Myrica pensylvanica, M. caroliniensis) is a native deciduous to evergreen shrub with dark green, often fragrant leaves. Inkberry (Ilex glabra) has glossy, dark green, semi-evergreen foliage and tiny white flowers that, if a male and female are both present, give way to black berries.
5. Multiflora rose (Rosa multiflora)
An extremely aggressive shrub or climbing rose, multiflora rose can grow up to 15 high and almost as wide. Its canes are often reddish and covered in curved thorns, and it has compound leaves with oval, serrated leaflets. Small, fragrant, white to pink flowers bloom in showy clusters in early summer, followed by bright red rose hips that persist through winter. Though it closely resembles native roses, look for fringed petioles to distinguish multiflora rose.
Similar native species include Virginia rose (R. virginiana) and swamp rose (R. palustris), both of which produce pink flowers.
6. Burning bush (Euonymus alatus)
Popular for its brilliant red fall foliage, burning bush is a medium to large deciduous shrub with a bushy habit. The opposite, elliptic leaves have finely toothed margins and are dark green in summer. Its inconspicuous green flowers give way to paired red-orange fruits that ripen to purple in autumn. But perhaps most distinctively, burning bush has prominent corky wings on its green to brown stems, giving it the common names winged burning bush and winged euonymus.
The native shrub red chokeberry (Aronia arbutifolia) also has vibrant fall color and red berries, and arrowwood viburnum (Viburnum dentatum) features beautiful rosy pink to red foliage in autumn.
7. Morrow’s honeysuckle (Lonicera morrowii)
The sweet fragrance of its creamy white to yellow tubular flowers make honeysuckle a spring sight to bring a smile to your face, but unfortunately, many species are invasive — including Morrow’s honeysuckle. The well-loved blossoms of this woody perennial shrub bloom in pairs beginning in early spring, and the red berries that follow last only from midsummer to fall. It has opposite, oblong, gray-green leaves that emerge early for a long season. All invasive bush honeysuckles have hollow stems.
Though a different genus altogether, bush honeysuckle (Diervilla sessilifolia) is a very similar native shrub, while limber honeysuckle (Lonicera dioica) is a true honeysuckle with a sprawling or climbing habit and striking red flowers.
Learn more about growing honeysuckle that’s not invasive.
8. Japanese knotweed (Fallopia japonica)
Japanese knotweed, a semi-woody herbaceous perennial, grows three to 10 feet tall and spreads by rhizomes and sprouting root fragments to rapidly form monocultures. It has smooth, hollow stems with swollen joints, somewhat resembling bamboo. The broad, alternate leaves have a flat base and pointed tip for a unique shape somewhere between an oval and a triangle. Creamy white flowers bloom in late summer, followed by small winged fruits containing glossy, dark, triangular seeds.
Similar native plants include sweet pepperbush (Clethra alnifolia) and goat’s beard (Aruncus dioicus).
9. Porcelainberry (Ampelopsis glandulosa)
Introduced as an ornamental ground cover, porcelainberry can also climb trees and forms dense mats over vegetation. The foliage looks a lot like grape leaves, with three to five lobes per leaf and slightly hairy undersides. The namesake iridescent blue and purple berries appear in clusters in autumn. To distinguish from grape vines, look for non-peeling bark and a white pith on porcelainberry.
Native grape vines, which look very similar, include summer grape (Vitis aestivalis) and fox grape (V. labrusca).
10. English ivy (Hedera helix)
A popular evergreen ground cover, English ivy forms dense, weed-excluding mats on the ground and climbs into tree canopies. Its waxy, dark green leaves range from unlobed to having as many as five lobes, though all have pale veins. Small, greenish-yellow flowers bloom in late summer under ideal conditions, and fleshy black fruits follow. Learn how to get rid of English ivy.
Bearberry (Arctostaphylos uva-ursi) is an attractive native evergreen ground cover, while Virginia creeper (Parthenocissus quinquefolia) makes for a good alternative vine.
Once you can recognize some of the most common and problematic invasive plants in Rhode Island gardens, you can start taking action from your own backyard to help save native ecosystems. Plus, you get to do some fun plant shopping along the way!