Invasive Shade-Tolerant Garden Plants in Maine

Maine’s beautiful forests and shaded areas are at risk from invasive plant species that can outcompete native flora and disrupt local ecosystems. These invasive plants, often introduced for their ornamental appeal, can spread rapidly in low-light conditions, affecting the natural balance of Maine’s ecosystems. Understanding these invasive species and choosing native alternatives is essential for preserving Maine’s natural beauty and biodiversity.

Common Buckthorn (Rhamnus cathartic)

List of Invasive Shade-Tolerant Garden Plants in Maine

1. Japanese Barberry (Berberis thunbergii)

• Description: A small, thorny shrub with bright red berries and small, glossy leaves. It is often planted for its ornamental value.

• Impact: Creates dense thickets in shaded areas, crowding out native plants and altering soil chemistry, which can negatively affect the surrounding ecosystem.

• Garden Alternative: Highbush Blueberry (Vaccinium corymbosum) - A native shrub that provides beautiful flowers, edible berries, and supports local wildlife.

2. Oriental Bittersweet (Celastrus orbiculatus)

• Description: A vigorous vine with bright orange berries and glossy green leaves, often used for decorative purposes.

• Impact: Rapidly covers and overwhelms native trees and shrubs, leading to significant ecological disruption in shaded environments.

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

3. Garlic Mustard (Alliaria petiolata)

• Description: A biennial herb with heart-shaped leaves and small white flowers, releasing a garlic-like odor when crushed.

• Impact: Outcompetes native vegetation in shaded woodlands, leading to reduced biodiversity and altered habitat structures.

• Garden Alternative: Wild Ginger (Asarum canadense) - A native ground cover with heart-shaped leaves that thrives in shaded environments and supports local ecosystems.

4. Japanese Knotweed (Fallopia japonica)

• Description: A robust perennial with large, heart-shaped leaves and clusters of small white flowers. It spreads aggressively, particularly in riparian areas.

• Impact: Forms dense stands that outcompete native vegetation, especially in shaded and riparian zones, reducing plant diversity.

• Garden Alternative: Joe-Pye Weed (Eutrochium purpureum) - A native perennial that supports pollinators and thrives in similar conditions without being invasive.

5. Common Buckthorn (Rhamnus cathartic)

• Description: A deciduous shrub or small tree with dark green leaves and small black berries. Initially introduced as a hedge plant, it has since become invasive.

• Impact: Invades woodlands and shaded areas, forming dense thickets that prevent native plants from growing.

• Garden Alternative: American Hazelnut (Corylus americana) - A native shrub that provides valuable habitat and food for wildlife, thriving in shaded environments.

6. Japanese Honeysuckle (Lonicera japonica)

• Description: A fast-growing vine with fragrant white to yellow flowers and dark green leaves. It is widely planted for its attractive blooms but is highly invasive.

• Impact: Forms dense mats that smother native plants, reducing biodiversity in shaded and woodland areas.

• Garden Alternative: Trumpet Honeysuckle (Lonicera sempervirens) - A native vine with red tubular flowers that attract hummingbirds and thrive in shaded conditions.

7. Norway Maple (Acer platanoides)

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

• Impact: Produces dense shade that suppresses native undergrowth, reducing biodiversity in forested and shaded areas.

• Garden Alternative: Sugar Maple (Acer saccharum) - A native tree that provides similar shade but supports a diverse understory of native plants.

8. Periwinkle (Vinca minor)

• Description: A low-growing, evergreen ground cover with glossy leaves and blue or purple flowers. It spreads quickly and is commonly used in shaded gardens.

• Impact: Its aggressive growth can overshadow and outcompete native ground covers, leading to reduced biodiversity in shaded areas.

• Garden Alternative: Bunchberry (Cornus canadensis) - A native ground cover that offers year-round appeal and supports local wildlife in shaded environments.

9. Japanese Yew (Taxus cuspidata)

• Description: A dense, evergreen shrub with dark green needles and red berries. It is often planted for hedges and ornamental purposes.

• Impact: It can spread into natural areas, displacing native plants and altering local ecosystems, especially in shaded forest edges.

• Garden Alternative: Eastern Hemlock (Tsuga canadensis) - A native evergreen that provides similar ornamental value and supports local wildlife.

Conclusion

Invasive shade-tolerant plants can significantly impact Maine’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 Maine’s landscapes.

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