The question of whether Veronica, commonly called Speedwell, is an invasive species or merely an aggressive garden weed is complicated because the genus is vast. Speedwells are found globally, and their behavior depends entirely on the specific species encountered. The term “Speedwell” refers to hundreds of different plants, some of which are highly prized ornamentals, while others are notorious for their rapid spread. Understanding the distinction between a legally defined invasive plant and an aggressively growing weed is the first step in managing these plants.
Defining the Speedwell Genus
The genus Veronica is the largest in the Plantaginaceae family, encompassing approximately 450 to 500 species of annuals, perennials, and subshrubs. These plants are primarily distributed across the temperate regions of the Northern Hemisphere, including Europe, Asia, and North America. They are characterized by small, four-lobed flowers, often appearing in shades of blue, purple, or white, and arranged in spikes or terminal clusters.
The leaves are typically opposite or subopposite on the stems, and their overall growth habit varies dramatically. Some species are low-growing, mat-forming groundcovers, while others are upright plants with prominent flower spikes. This wide spectrum of forms, from delicate wildflowers to robust garden subjects, is the source of the varied reputation Speedwell holds among gardeners.
The Invasive vs. Aggressive Distinction
The confusion surrounding Speedwell’s status stems from a misunderstanding of the term “invasive” in an ecological and regulatory context. An invasive species is non-native and causes environmental or economic harm, often resulting in regulation by authorities. Few, if any, Veronica species meet this strict legal definition, meaning they are not typically found on official invasive species lists.
The species that cause gardeners concern are better classified as aggressive weeds. The most common offenders are non-native species like Veronica filiformis (Creeping Speedwell) and Veronica persica (Persian Speedwell). Creeping Speedwell spreads rapidly by creating dense, ground-hugging mats and rooting easily at its stem nodes (stolonization). Even small pieces of stem broken off by mowing can root and establish new plants.
These aggressive species are difficult to eradicate because their low-growing habit allows them to evade mower blades and compete effectively with turfgrass. Persian Speedwell reproduces prolifically by producing numerous seeds. This combination of vegetative spread and rapid reseeding allows these weedy forms of Speedwell to quickly colonize and dominate lawns and garden beds.
Control Methods for Weedy Species
Managing aggressive Speedwell species requires a combination of cultural and, sometimes, chemical practices tailored to their growth habit. Non-chemical control methods are often the most practical. Manual removal of weedy species like Creeping Speedwell is effective, but it is important to extract all pieces of the rhizomes and stems, as fragments can easily re-root.
Improving the density and health of a lawn is the best defense against Speedwell establishment. Proper cultural practices, such as raising the mowing height, regular fertilization with high-nitrogen products, and adequate watering, help turfgrass outcompete the low-growing weed. For garden beds, deep tilling can inhibit the germination of small-seeded Speedwell species.
When non-chemical methods are insufficient, targeted chemical control can be considered. Weedy Speedwell species are resistant to common herbicides like 2,4-D, which is often found in broadleaf weed killers. Selective post-emergent herbicides designed to control broadleaf weeds in turfgrass are available, but users must follow all label instructions carefully to ensure the product is effective.
Recommended Ornamental Varieties
The aggressive spreading habits of weedy Speedwells do not apply to the many non-aggressive species cultivated for ornamental purposes. These varieties are typically clump-forming perennials that add vertical interest to garden borders without escaping their boundaries. They are valued for their long bloom times and striking flower spikes.
Species such as Veronica spicata (Spiked Speedwell) and Veronica longifolia (Long-leaf Speedwell) are popular choices for their upright growth habit. Cultivars like ‘Royal Candles’ and ‘Eveline’ provide dense spikes of deep blue or lavender-pink flowers that are perfect for cutting. Other well-behaved varieties, such as Veronica prostrata (Prostrate Speedwell), offer a controlled spreading habit that works well as a tidy groundcover.