Common groundsel (Senecio vulgaris) is an annual flowering herb that is related to daisies. Though the flowers resemble immature dandelions, they never “open” the way those other yellow flowers do. Canaries and finches are particularly fond of this plant’s seeds and the larvae of several moth species eat the greens. Common groundsel is toxic to humans and some livestock.
I. Appearance and Characteristics
Senecio vulgaris, often known by the common names groundsel and old-man-in-the-spring, is a flowering plant in the family Asteraceae. It is an annual herb, native to the Palaearctic and widely naturalised as a ruderal species in suitable disturbed habitats worldwide.
Senecio vulgaris is an erect herbaceous annual growing up to 16 inches (41 cm) tall. The inflorescences usually lack ray florets, the yellow disc florets mostly hidden by the bracts giving the flowers an inconspicuous appearance. Senecio vulgaris is very similar to Senecio viscosus but S. vulgaris does not have the glandular hairs and ray florets found in S. viscosus.
Leaves and stems
Upper leaves of Senecio vulgaris are sessile, lacking their own stem (petiole), alternating in direction along the length of the plant, two rounded lobes at the base of the stem (auriculate) and sub-clasping above. Leaves are pinnately lobed and +2.4 inches (61 mm) long and 1 inch (25 mm) wide, smaller towards the top of the plant. Leaves are sparsely covered with soft, smooth, fine hairs. Lobes typically sharp to rounded saw-toothed.
The hollow stems branch at the tops and from the base. Stems and leaves can both host the Cineraria leaf rust.
Flowers
Open clusters of 10 to 22 small cylinder shaped rayless yellow flower heads 1⁄4 to 1⁄2 inch (6 to 13 mm) with a highly conspicuous ring of black tipped bracts at the base of the inflorescence as is characteristic of many members of the genus Senecio. There is a radiate form of Senecio vulgaris, which is the result of cross pollination with the closely related Oxford ragwort, Senecio squalidus.
Seeds
The name for the genus Senecio is probably derived from senex (an old man), in reference to its downy head of seeds; “the flower of this herb hath white hair and when the wind bloweth it away, then it appeareth like a bald-headed man” and like its family, flowers of Senecio vulgaris are succeeded by downy globed heads of seed. The seeds are achene, include a pappus and become sticky when wet. Laboratory tests have suggested maximum seed scattering distances of 4.2 and 4.6 yd (3.8 and 4.2 m) at wind speeds of 6.8 and 10.2 mph (10.9 and 16.4 km/h) respectively (affected by plant height), suggesting that it was more than wind that spread these groundsel seeds throughout the world.
The average weight of 1000 seeds is 0.21 gram (2,200,000 seeds per pound) and experienced a 100% germination success before drying and storage and an 87% germination success after drying and 3 years of cool dry storage. In simple models for seed emergence prediction, soil thermal time did not predict the timing and extent of seedling emergence as well as hydrothermal time (warm rain).
Roots
The root system consists of a shallow taproot. This plant spreads by reseeding itself.
Groundsel acts as a host for the fungus that causes black root rot in peas, alfalfa, soybeans, carrots, tomatoes, red clover, peanuts, cucurbits, cotton, citrus, chickpeas, and several ornamental flowering plants; a list of flowering plants that can host their own fungus as well.
Toxicity
In the United States, Senecio vulgaris has been listed as a noxious weed, being both non-indigenous to most if not all of the Americas and having a reputation for being hepatotoxic to livestock and to humans.
Senecio vulgaris is a frost-resistant deciduous annual plant that grows in disturbed sites, waste places, roadsides, gardens, nurseries, orchards, vineyards, landscaped areas, agricultural lands, at altitudes up to 1,600 feet (500 m) and is, additionally, self-pollinating producing 1,700 seeds per plant with three generations per year. Seeds are dispersed by wind and also cling to clothing and animal fur, and as contaminates of commercially exchanged seeds; the distribution of this plant throughout the world has been difficult if not impossible to contain.
II. How to Grow and Care
Sunlight
Common groundsel thrives best in full sun conditions, where it can receive a substantial amount of direct light throughout the day. This plant’s ability to grow in full sun promotes vigorous growth and enhances its overall health. While common groundsel can withstand partial sun, implying some tolerance to lower light levels, its growth may not be as robust compared to being under optimal light exposure. Adaptive traits, such as leaf orientation, might adjust under varying light to maximize light capture. Outdoor cultivation should be in locations where common groundsel receives unfiltered sunlight for the majority of the day, although it can manage with some shade. Optimal placement is crucial for promoting its health and vitality.
Watering
Originating from temperate regions, common groundsel is adapted to moderate moisture levels, thriving in environments that mimic its native habitat’s balanced water availability. It exhibits a preference for consistent soil moisture without being waterlogged, showcasing moderate drought tolerance. Care should involve watering every week to maintain this equilibrium. As an herbaceous weed often found outdoors, common groundsel has a notable ability to compete for water resources during its rapid growth cycle, even in varied climate zones.
Propagation
Common groundsel is primarily propagated by sowing seeds in the spring. This process is typically easy, with successful propagation indicated by seedling emergence. No specific tips are required for effective propagation.
Transplanting
The optimum period for transplanting common groundsel is between S1-S3, as this is when the plant establishes quickest. This plant prefers well-drained soil and a sunny location. Remember, common groundsel does not take kindly to excessive root disturbance, so handle it with care.