Invasive Shade-Tolerant Garden Plants in Rhode Island

Rhode Island’s unique coastal woodlands, river valleys, and shaded gardens are susceptible to invasive plant species that thrive in low-light environments. These plants can quickly outcompete native vegetation, leading to a loss of biodiversity and altering local ecosystems. By identifying and managing these invasive plants, and opting for native alternatives, gardeners can help preserve Rhode Island’s natural beauty.

Black Swallowwort (Cynanchum louiseae)

List of Invasive Shade-Tolerant Garden Plants in Rhode Island

1. Japanese Barberry (Berberis thunbergii)

• Description: A thorny shrub with bright red berries and small, glossy leaves, often used in landscapes for its vibrant color.

• Impact: Forms dense thickets that alter soil pH and provide a habitat for ticks, contributing to an increased risk of Lyme disease.

• Garden Alternative: Highbush Blueberry (Vaccinium corymbosum) - A native shrub with edible berries that supports local wildlife and thrives in Rhode Island's acidic soils.

2. Black Swallowwort (Cynanchum louiseae)

• Description: A twining vine with dark purple, star-shaped flowers, commonly found in shaded areas and open fields.

• Impact: Rapidly spreads in shaded areas, choking out native plants and posing a threat to monarch butterfly populations, as it is toxic to their larvae.

• Garden Alternative: Virginia Clematis (Clematis virginiana) - A native vine with clusters of white flowers that provide similar coverage without the invasiveness.

3. Japanese Knotweed (Fallopia japonica)

• Description: A fast-growing perennial with large, heart-shaped leaves and small white flowers. It thrives in moist, shaded environments, especially near waterways.

• Impact: Forms dense thickets that crowd out native species, particularly in riparian zones, leading to erosion and habitat loss.

• Garden Alternative: Red Osier Dogwood (Cornus sericea) - A native shrub that helps stabilize soil and provides winter interest with its red stems.

4. Norway Maple (Acer platanoides)

• Description: A large deciduous tree with broad, dark green leaves, often planted for its dense shade.

• Impact: Produces dense shade that suppresses native undergrowth, reducing plant diversity in Rhode Island’s woodlands.

• Garden Alternative: Sugar Maple (Acer saccharum) - A native tree that offers beautiful fall color and supports a diverse understory of native plants.

5. English Ivy (Hedera helix)

• Description: An evergreen vine with dark green, lobed leaves, commonly used for ground cover or climbing.

• Impact: Smothers native plants and trees, reducing biodiversity, and causing damage to structures and natural habitats in Rhode Island’s shaded areas.

• Garden Alternative: Virginia Creeper (Parthenocissus quinquefolia) - A native vine that provides similar coverage with vibrant fall colors, supporting local wildlife.

6. Tree-of-Heaven (Ailanthus altissima)

• Description: A rapidly growing deciduous tree with large, compound leaves, often found in disturbed areas.

• Impact: Invades shaded areas and produces chemicals that inhibit the growth of nearby plants, leading to monocultures.

• Garden Alternative: American Hornbeam (Carpinus caroliniana) - A native tree that thrives in shade and provides valuable wildlife habitat.

7. Oriental Bittersweet (Celastrus orbiculatus)

• Description: A climbing vine with bright orange berries and glossy green leaves, often planted for ornamental purposes.

• Impact: Overwhelms native trees and shrubs, leading to their decline, particularly in Rhode Island’s coastal forests.

• Garden Alternative: American Bittersweet (Celastrus scandens) - A native vine with similar ornamental value but without the invasive tendencies.

8. Japanese Stiltgrass (Microstegium vimineum)

• Description: A thin, annual grass with pale green leaves that often invades shaded, disturbed areas.

• Impact: Forms dense mats that crowd out native plants, leading to reduced biodiversity and altered soil conditions in Rhode Island's forests.

• Garden Alternative: Pennsylvania Sedge (Carex pensylvanica) - A native sedge that thrives in shade and provides similar ground coverage.

9. Multiflora Rose (Rosa multiflora)

• Description: A thorny shrub with clusters of small white flowers and bright red rose hips, initially introduced as a living fence.

• Impact: Forms dense thickets in shaded areas, outcompeting native plants and reducing habitat quality for wildlife.

• Garden Alternative: Pasture Rose (Rosa carolina) - A native rose with fragrant pink flowers that supports pollinators and thrives in similar conditions.

Conclusion

Invasive shade-tolerant plants can significantly impact Rhode Island’s ecosystems by outcompeting native species and altering local habitats. By choosing native, non-invasive alternatives, gardeners can help maintain ecological balance, support local wildlife, and preserve the natural beauty of Rhode Island’s landscapes.

For more information and to connect with other gardening enthusiasts, join our Facebook group: Shade Gardening.