Aggressive Competitive Plants

Wildflowers

• While many wildflowers are cultivated as ornamental plants, some grow competitively and push out other species if left untended. Ground ivy (Glechoma hederacea) grows in a prostrate, creeping form. This perennial wildflower grows up to 8 inches tall, has leaves with scalloped margin and blooms from spring through midsummer with clusters of blue-purple flowers. This European native spreads quickly using its creeping stems. Its natural habitat includes shaded sites, thickets and lawns. Crimson bee balm (Monarda didyma) grows from 2 to 5 feet tall. This perennial blooms with aromatic, bright-red flowers from summer through fall and has serrated foliage. It grows best in full sun and prefers fertile, acidic and moist soil but spreads more quickly when growing in shaded sites. Crimson bee balm grows naturally in thickets, ditches and along streambanks and spreads rapidly with its invasive roots.

Ground Covers

• Ground covers can be valuable in the landscape as they slow erosion and reduce runoff, but some species grow aggressively. Bishop's weed (Aegopodium podograria) grows from 8 to 10 inches tall and spreads aggressively through rhizomes. This deciduous plant is cultivated as an ornamental ground cover. It has aromatic foliage and produces small blossoms from spring through summer. Bishop's weed grows well in partial to full shade and tolerates a range of sites, from clay to sand. Bugleweed or ajuga (Ajuga reptans) is also grown as an ornamental ground cover. This evergreen spreads rapidly and prefers partial to full shade and sandy, well-drained soil. Bugleweed has lustrous green foliage, blooms with purple-blue flowers in spring, and invades areas with its aggressive roots.

Perennials

• Perennials grows for at least three years; some species grow for much longer -- and very vigorously. Lamb's ear (Stachys byzantine) grows from12 to 15 inches tall. This perennial spreads rapidly through creeping, rooting stems. Lamb's ear is usually grown for its silver-green, fuzzy leaves but does bloom with pink to purple flowers in midsummer. It prefers full sun and well-drained soil. Purple loosestrife (Lythrum salicaria) has been classified as a noxious weed in several states due to its aggressive tendencies. This perennial grows from 3 to 5 feet tall and thrives in full sun and moist to wet soil. It blooms in summer with tall, pink-purple spikes and tends to crowd out other vegetation in wetlands.

Shrubs

• Some shrub species can crowd out other plants or have competitive roots. Non-native buckthorns such as the common buckthorn and glossy buckthorn (Rhamnus cathartica and frangula) have competitive root systems and tend to crowd or shade out indigenous plants. The common buckthorn grows quickly from 18 to 25 feet tall and has deciduous, dark-green foliage with serrated margins. It produces black, bird-attracting, but toxic, berries and thrives in full sun and a range of soils. Glossy buckthorn grows to 15 feet tall and produces red-to-black drupes that last through fall. Not all aggressive, competitive plants are non-native. Yucca shrubs (Yucca spp.) also have invasive roots but many types are native to the southwestern U.S. These evergreen shrubs grow in a range of sizes and shapes, but all have thick, pointed foliage. They prefer full sun and well-drained soil, and many produce flowers atop tall stalks.