Invasive Shade-Tolerant Garden Plants in Colorado

Colorado’s diverse environments, from its mountainous regions to its riverbanks, are increasingly impacted by several garden plants that thrive in shaded conditions and have become invasive. These plants, often introduced for their aesthetic appeal and resilience, can escape gardens and spread into natural areas, outcompeting native species and disrupting ecosystems. By understanding these invasive plants and opting for native alternatives, gardeners can help maintain Colorado’s natural beauty and ecological balance.

Yellow Archangel (Lamiastrum galeobdolon)

List of Invasive Shade-Tolerant Garden Plants in Colorado

1. English Ivy (Hedera helix)

• Description: English Ivy is a climbing vine with dark green, lobed leaves. It’s commonly used as ground cover or for covering walls and fences in shaded garden areas.

• Impact: English Ivy spreads aggressively, smothering native plants and trees, and leading to the decline of forest health, especially in shaded forest environments.

• Garden Alternative: Native Creeping Mahonia (Mahonia repens) - A native ground cover with holly-like leaves and yellow flowers that thrives in shade without invasive tendencies.

2. Japanese Knotweed (Fallopia japonica)

• Description: Japanese Knotweed is a robust, perennial herb with large, heart-shaped leaves and tall, bamboo-like stems. It is often used in gardens for its fast growth and ability to quickly cover ground.

• Impact: It spreads rapidly and forms dense thickets that can overtake native vegetation and disrupt stream banks and shaded woodland areas.

• Garden Alternative: Streambank Wildrye (Elymus lanceolatus ssp. lanceolatus) - A native grass that stabilizes soil along stream banks and thrives in shaded areas.

3. Common Privet (Ligustrum vulgare)

• Description: Common Privet is an evergreen shrub with small, white flowers and dark berries. It is used as a hedge or ground cover in shaded garden areas.

• Impact: It can spread into natural areas, forming dense thickets that displace native plants and reduce habitat quality for wildlife.

• Garden Alternative: Mountain Mahogany (Cercocarpus montanus) - A native shrub with attractive foliage and resilience, providing habitat and food for wildlife.

4. Siberian Elm (Ulmus pumila)

• Description: Siberian Elm is a fast-growing tree with small, serrated leaves and a broad canopy. It’s often planted for quick shade and windbreaks.

• Impact: This tree spreads rapidly and can form dense stands that outcompete native trees and disrupt local ecosystems, particularly in shaded forest edges.

• Garden Alternative: Gambel Oak (Quercus gambelii) - A native oak tree that provides excellent shade and supports local wildlife without becoming invasive.

5. Russian Olive (Elaeagnus angustifolia)

• Description: Russian Olive is a tree or large shrub with silvery leaves and small, fragrant flowers. It’s often planted for its attractive foliage and tolerance of various soil conditions.

• Impact: It invades riparian areas, displacing native vegetation and altering soil conditions, which can harm local ecosystems.

• Garden Alternative: Boxelder (Acer negundo) - A native tree that offers shade and supports wildlife without the invasive qualities of Russian Olive.

6. Purple Loosestrife (Lythrum salicaria)

• Description: Purple Loosestrife is a perennial with tall spikes of purple flowers and lance-shaped leaves. It is often planted for its vibrant blooms in garden beds.

• Impact: It spreads aggressively in wetlands and along stream banks, displacing native plants and reducing biodiversity.

• Garden Alternative: Great Blue Lobelia (Lobelia siphilitica) - A native plant with striking blue flowers that thrives in moist, shaded areas and supports local pollinators.

7. Yellow Archangel (Lamiastrum galeobdolon)

• Description: Yellow Archangel is a vigorous ground cover with yellow flowers and variegated leaves, often used in shaded garden beds for its decorative appearance.

• Impact: It spreads quickly, forming dense mats that outcompete native plants, especially in shaded woodland areas.

• Garden Alternative: Woodland Strawberry (Fragaria vesca) - A native ground cover with edible berries that thrives in shade and is less aggressive.

Conclusion

While these invasive plants are commonly used in shaded gardens across Colorado, their tendency to spread and outcompete native species can cause significant harm to natural ecosystems. By choosing native, non-invasive alternatives, gardeners can help protect Colorado’s unique landscapes, support local wildlife, and maintain the state’s natural beauty.