Invasive Shade-Tolerant Garden Plants in Montana

Montana's diverse ecosystems, from its mountainous regions to shaded woodlands, are susceptible to invasive plant species that can thrive in low-light environments. These invasive plants can spread rapidly, outcompeting native vegetation and disrupting local habitats. Identifying these plants and selecting native alternatives is essential for preserving Montana’s natural beauty and biodiversity.

Leafy Spurge (Euphorbia esula)

List of Invasive Shade-Tolerant Garden Plants in Montana

1. Spotted Knapweed (Centaurea stoebe)

• Description: A perennial herb with purple, thistle-like flowers, often found in disturbed areas including shaded regions.

• Impact: Spotted Knapweed outcompetes native plants, reducing biodiversity and altering soil chemistry, particularly in shaded forest edges and grasslands.

• Garden Alternative: Fireweed (Chamerion angustifolium) - A native plant with bright pink flowers that supports pollinators and thrives in similar conditions without becoming invasive.

2. Common Tansy (Tanacetum vulgare)

• Description: A perennial herb with bright yellow button-like flowers and feathery leaves, commonly found in disturbed and shaded areas.

• Impact: Common Tansy forms dense stands that crowd out native plants, reducing plant diversity and affecting local ecosystems.

• Garden Alternative: Goldenrod (Solidago canadensis) - A native perennial with yellow flower clusters that supports pollinators and thrives in similar habitats.

3. Dalmatian Toadflax (Linaria dalmatica)

• Description: A perennial herb with bright yellow, snapdragon-like flowers and waxy leaves, often found in disturbed areas.

• Impact: Dalmatian Toadflax spreads aggressively in shaded and open areas, outcompeting native plants and reducing biodiversity.

• Garden Alternative: Yellow Monkeyflower (Mimulus guttatus) - A native plant with similar yellow flowers that thrives in moist, shaded areas.

4. Leafy Spurge (Euphorbia esula)

• Description: A perennial herb with narrow leaves and small, greenish-yellow flowers, known for its milky sap.

• Impact: Leafy Spurge forms dense monocultures that displace native vegetation, especially in shaded grasslands and riparian zones.

• Garden Alternative: Prairie Smoke (Geum triflorum) - A native perennial with unique pink flowers that support pollinators and thrive in similar environments.

5. Oxeye Daisy (Leucanthemum vulgare)

• Description: A perennial herb with white petals and yellow centers, often found in gardens and shaded meadows.

• Impact: Oxeye Daisy spreads aggressively, forming dense patches that crowd out native wildflowers and reduce biodiversity.

• Garden Alternative: Shasta Daisy (Leucanthemum × superbum) - A cultivated alternative that offers similar flowers but without the invasive tendencies.

6. Yellow Toadflax (Linaria vulgaris)

• Description: A perennial herb with bright yellow flowers and a long spur, commonly found in disturbed and shaded areas.

• Impact: Yellow Toadflax invades grasslands and shaded areas, forming dense stands that outcompete native plants.

• Garden Alternative: Golden Banner (Thermopsis montana) - A native plant with similar yellow flowers that supports local wildlife and thrives in similar conditions.

7. Houndstongue (Cynoglossum officinale)

• Description: A biennial herb with reddish-purple flowers and large, hairy leaves, often found in disturbed, shaded areas.

• Impact: Houndstongue forms dense stands that reduce native plant diversity and are toxic to livestock.

• Garden Alternative: Penstemon (Penstemon spp.) - A native perennial with attractive flowers that support pollinators and thrive in similar shaded environments.

8. Japanese Knotweed (Fallopia japonica)

• Description: A robust perennial with large, heart-shaped leaves and clusters of small white flowers, known for its aggressive growth.

• Impact: Japanese Knotweed forms dense thickets in shaded riparian areas, outcompeting native vegetation and reducing biodiversity.

• Garden Alternative: Western Columbine (Aquilegia formosa) - A native plant with red and yellow flowers that supports pollinators and thrives in similar conditions without becoming invasive.

9. Canada Thistle (Cirsium arvense)

• Description: A perennial herb with spiny leaves and purple flowers, often found in disturbed and shaded areas.

• Impact: Canada Thistle spreads rapidly, forming dense stands that displace native plants and reduce biodiversity.

• Garden Alternative: Elk Thistle (Cirsium foliosum) - A native thistle that supports pollinators and wildlife without invasive properties.

Conclusion

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

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