The appearance of delicate blue flowers in a lawn or garden often signals a welcome sight, yet these blossoms frequently belong to persistent and invasive plants. A “weed” is simply a plant growing where it is not wanted, and many nuisance species display attractive blue or violet blooms. Recognizing these plants by their specific features, growth habits, and leaf structures is the first step in managing their aggressive spread.
Identifying Characteristics of Common Blue Weeds
Identifying blue-flowered weeds requires attention to their physical structure and preferred growing conditions. The overall growth habit differentiates between plants that spread low along the ground and those that grow upright. Some weeds use runners that root at the nodes to form dense mats, while others establish a deep taproot for perennial survival.
Leaf structure provides distinct markers, ranging from rounded, scalloped edges to deeply lobed leaves. Examining the stem is also useful; plants in the mint family, for instance, are characterized by a square stem. The specific environment where the plant thrives, such as moist shade or dry, disturbed soil, helps narrow down identification possibilities.
Flower structure is another identifier, as blooms can be solitary or clustered, varying significantly in petal arrangement and size. Some flowers are tiny, four-lobed, and nearly flat, while others are small, tubular, and bunched in leaf axils.
Major Blue-Flowered Weeds and Their Names
Creeping Charlie (Glechoma hederacea)
One notorious blue-flowered invader is Creeping Charlie (Glechoma hederacea), a low-growing perennial in the mint family. It is easily identified by its rounded, kidney-shaped leaves with scalloped edges and its signature square stem. When crushed, the foliage emits a distinct, mint-like aroma. Small, bluish-purple, funnel-shaped flowers appear close to the ground in spring and early summer. This plant thrives in moist, shaded areas, rapidly spreading via runners that root at every joint.
Chicory (Cichorium intybus)
Chicory (Cichorium intybus) is a common roadside and garden weed, known for its milky sap and tough, woody stem. This perennial or biennial forms a basal rosette of deeply lobed leaves in its first year. In the second year, it sends up a tall, rigid flower stalk that can reach several feet in height. Numerous bright blue, daisy-like flowers bloom along the stem, notable for opening in the morning and often closing by midday. Chicory is frequently encountered in disturbed areas due to its deep, resilient taproot.
Speedwell (Veronica species)
The genus Veronica, commonly known as Speedwell, includes several common lawn and garden weeds, such as Slender Speedwell (Veronica filiformis) and Corn Speedwell (Veronica arvensis). These plants are low-growing and sprawling, featuring tiny, four-lobed flowers, often bright blue with a white center. The blooms appear solitary or in small spikes. Slender Speedwell is an aggressive perennial that forms dense mats and roots readily at the nodes of its creeping stems.
Asiatic Dayflower (Commelina communis)
The Asiatic Dayflower (Commelina communis) is a summer annual found in moist, fertile soils and disturbed areas. Its unique flowers are short-lived, consisting of two prominent, bright blue petals and one much smaller, pale white petal underneath. The plant has hairless, lance-shaped leaves with parallel veins that clasp the stem with a membranous sheath. The Asiatic Dayflower has a sprawling habit, with stems that can root at the joints, allowing it to colonize an area quickly.
Control and Management Strategies
Successful control of these blue-flowered weeds begins with improving the overall health of the desired vegetation, particularly turfgrass. Maintaining a dense, vigorously growing lawn through proper cultural practices—such as correct mowing height, aeration, and fertilization—helps the grass outcompete low-growing weeds. Since many blue-flowered weeds thrive in moist, compacted, and shady areas, correcting poor drainage and pruning trees to increase light penetration reduces their advantage.
For small, isolated patches, mechanical removal is a viable option, but it requires diligent effort to ensure the entire root system is eliminated. Plants with deep taproots, like Chicory, must be dug out completely. Creeping species require the removal of all runners and rooted nodes to prevent regrowth from small fragments. Bagging and disposing of the pulled material is advisable, as stems and seeds can regenerate in a compost pile.
For more extensive infestations, selective broadleaf herbicides offer a targeted chemical solution. Herbicides containing active ingredients such as triclopyr, 2,4-D, and dicamba are commonly used to manage these weeds without harming the surrounding turf. Application is most effective in the fall, as perennial weeds actively transport nutrients to their roots for winter storage, allowing the herbicide to be drawn down for better control.