The Blue Star Creeper is a popular, low-growing groundcover known for its dense mat of tiny foliage and delicate, star-shaped blue flowers. Gardeners often choose it to fill spaces between stepping stones or as a lawn alternative, attracted by its resilient nature and charming appearance. However, the plant is also notorious for its rapid spread, leading many to question its classification: does this plant behave as a simple aggressive spreader, or is it a true invasive threat?
Defining Blue Star Creeper
The plant commonly known as Blue Star Creeper is scientifically identified as Isotoma fluviatilis or sometimes Laurentia fluviatilis. It is a herbaceous perennial that forms a lush, evergreen carpet, typically reaching a height of only two to three inches above the soil surface. This species originates in the damp, temperate regions of Australia and New Zealand.
Its foliage consists of tiny, bright green leaves, creating a fine-textured mat. The namesake flowers are pale blue or white, small, and five-petaled, appearing profusely from late spring into summer. This low-growing habit, coupled with its ability to withstand some foot traffic, makes it a favored plant for filling crevices in patios and walkways.
Aggressive Spreader vs. True Invasive Threat
The distinction between a plant that is aggressive and one that is invasive is based on its ecological impact beyond the garden setting. An aggressive plant spreads rapidly and vigorously within a cultivated landscape, often outcompeting nearby ornamental plants. While this behavior can be troublesome for gardeners, it is confined to the immediate planting area.
In contrast, a plant is classified as “invasive” only when it is non-native and causes significant environmental or economic harm by displacing native species in natural ecosystems. This classification is typically determined by state or federal authorities and results in the plant being listed as prohibited. Blue Star Creeper is generally considered an aggressive groundcover in the garden, spreading quickly through runners and rooting stems. In most regions of North America, it is not officially listed as a true invasive species, meaning it does not typically escape cultivation to colonize natural habitats.
Understanding Its Growth Dynamics
The rapid coverage achieved by Blue Star Creeper is primarily due to its efficient method of vegetative reproduction. The plant spreads by sending out slender, creeping stems that root easily at the nodes where they touch the soil. These stems create a dense, intertwined network just beneath the surface, quickly expanding the plant’s footprint.
The plant’s preference for consistently moist, well-drained soil and partial shade environments further fuels its speed of growth. In ideal, well-watered conditions, a small patch can expand by 18 inches or more within a single growing season. Its resilience and tolerance for being walked on means the plant is not easily deterred from spreading across paths or between pavers.
Management and Containment
Containing the spread of Blue Star Creeper requires understanding its shallow, rooting nature. The most effective long-term strategy involves installing physical barriers, such as deep landscaping edging, around the desired planting area. This edging material should extend at least a few inches into the soil to block the creeping stems from spreading into adjacent beds or lawns.
Regular, selective weeding is necessary to control its expansion, focusing on manually pulling up the rooted runners that stray beyond the boundaries. Because the stems root at the nodes, it is important to remove the entire trailing piece to prevent regrowth from remaining segments. For areas where its spread is contained, routine trimming can help maintain a neat appearance. Chemical control, using a non-selective herbicide, can be used as a last resort, but caution must be exercised to avoid damaging surrounding plants.