Not all invasive weeds present themselves with a rough, unkempt appearance; some arrive adorned with stunning purple flowers that can outshine your prized perennials. Unfortunately, these beautiful blooms often disguise their aggressive nature, suppressing desirable plants and taking over your landscape. Invasive species such as purple deadnettle, bull thistle, and purple loosestrife may seem appealing, but their presence can have detrimental effects on your garden.
The Risks of Invasive Plants
While some plants may look like charming additions to your garden, they can be harmful to both your landscape and your pets. Invasive plants not only suppress desirable shrubbery and turfgrass but also pose risks to your furry friends if they contain toxic chemicals or spines. Moreover, even when frost kills off the visible parts of these invasive weeds, their seeds and root fragments often survive, allowing them to reestablish themselves in your garden.
To protect your landscape, it’s crucial to recognize the purple bloomers that might seem harmless but are, in fact, invasive plants. Here’s a closer look at some of the most problematic offenders.
Common Invasive Purple-Blooming Weeds
1. Purple Deadnettle (Lamium purpureum)
Purple deadnettle is a sneaky winter annual that can wreak havoc on your lawn. It germinates in the fall, producing a rosette of purple-tinted, heart-shaped leaves with toothed margins. By spring, it boasts pale green, hairy undersides and blooms with two-lipped purple flowers that release seeds in early summer. Found in disturbed garden soils or mulched areas, purple deadnettle can be manually pulled or tilled to prevent its spread since its roots do not extend deeper than a few inches.
2. Henbit (Lamium amplexicaule)
Often confused with purple deadnettle, henbit is another winter annual that features square stems. Its smaller, more rounded blades are densely fuzzy, with no petioles or minty aroma. Henbit’s purple flowers have dark mottled spots and attract hummingbirds and long-tongued bees. Found in bare patches with moist soil, it can be effectively managed by hoeing or pulling it out before it sets seed.
3. Ground Ivy (Glechoma hederacea)
Also known as creeping Charlie, ground ivy has become a scourge in many lawns across the U.S. It features heart-shaped leaves with scalloped edges and blooms lavender-to-blue tubular flowers from March to July. Ground ivy spreads aggressively through stolons, creating thick mats that suppress surrounding vegetation. Glyphosate is often required for control, as even small fragments can resprout.
4. Common Mallow (Malva neglecta)
Common mallow typically infests poorly maintained gardens. This low-growing plant features kidney-shaped, wrinkled leaves attached to long petioles. Its five-petalled, papery white to pale purple flowers bloom from May to October. Common mallow spreads through seeds and plant parts, making it essential to maintain healthy lawns to prevent its establishment.
5. Musk Thistle (Carduus nutans)
Musk thistle is a biennial plant that can produce over 20,000 seeds, quickly outcompeting native vegetation. The first year shows spiny, lance-like rosettes, while the second year produces red-to-violet disk-shaped flowers from May to August. Preventing its spread requires multiple mowings before it flowers.
6. Bull Thistle (Cirsium vulgare)
Bull thistle is prevalent across the U.S. and features gumdrop-shaped purple flowerheads. It grows a 3-foot-wide rosette in its first year and can reach 7 feet tall when mature. Mowing before the flowers set seeds is crucial for control, as bull thistles do not reproduce vegetatively.
7. Canada Thistle (Cirsium arvense)
Unlike other thistles, Canada thistle relies on a dense network of lateral roots and can thrive in various soil types. Its lavender-to-white flowerheads persist through October. To manage its spread, a combination of mowing and herbicide applications is necessary.
8. Purple Loosestrife (Lythrum salicaria)
Purple loosestrife is a vibrant but invasive plant found in wet soils. With spikes of purple flowers and a capacity to produce numerous stems, it can displace native vegetation. Its purchase is illegal in several states due to its invasive nature.
9. Creeping Speedwell (Veronica filiformis)
Creeping speedwell is sometimes sold as an ornamental groundcover but is considered invasive in West Virginia. It produces violet blooms and spreads quickly through rhizomes, making it difficult to eliminate without herbicides.
10. Germander Speedwell (Veronica chamaedrys)
Another troublesome speedwell species, Germander speedwell thrives in shaded, sandy soils. Its clusters of small violet flowers can easily be mistaken for creeping speedwell, but it features larger leaves and a more upright habit.
11. Great Burdock (Arctium lappa)
Originally from Eurasia, great burdock is a biennial wildflower that becomes invasive in the U.S. Its first year consists of a leafy rosette, but in its second year, it produces large leaves and purple flowers that turn into spiny burrs, spreading aggressively.
12. Purple Crown-Vetch (Securigera varia)
Once admired for its soil erosion control, purple crown-vetch has become invasive due to its prolific seeding and long rhizomes. It produces clusters of purplish-pink flowers and can grow into dense thickets.
13. Creeping Bellflower (Campanula rapunculoides)
Creeping bellflower is often misidentified as non-invasive ladybells. Its urn-shaped purple flowers can dominate gardens, and it spreads through rhizomes, making control difficult.
14. Healall (Prunella vulgaris)
Common selfheal is a creeping weed that flourishes in shady areas, sporting puckered ovate leaves and purple-mottled flowers in summer. Manual removal is the best method for control.
15. Bittersweet Nightshade (Solanum dulcamara)
This woody vine thrives in moist, disturbed soils and can climb trees. Its tubular lavender flowers and red berries spread aggressively, often through bird dissemination.
16. Field Garlic (Allium vineale)
Field garlic is often overlooked due to its chive-like leaves, but it releases a pungent odor when disturbed. Its lavender inflorescences develop into star-shaped flowers, and digging it out before bulb production can help manage its spread.
17. Spotted Knapweed (Centaurea maculosa)
This invasive weed thrives in dry, sandy soils and can grow over 2 feet tall. Its thistle-shaped purple flowers bloom from July to September and can quickly dominate a landscape.
Conclusion
Identifying and managing invasive purple-blooming weeds is essential to maintaining a healthy and beautiful garden. These weeds may initially seem attractive, but their aggressive nature can lead to significant challenges. Regular monitoring, manual removal, and, when necessary, herbicide applications are critical strategies for keeping these invaders at bay. By staying informed and proactive, you can protect your landscape from the hidden dangers of these invasive plants.
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