Common groundsel or old-man-of-the-spring (Senecio vulgaris) is found nearly everywhere in California. It is most prolific during the cooler times of the year, but can be found year-round near the coast or in shady areas. Although common groundsel grows best in moist fertile soil, it can grow in more trying environments such as along roadsides and other disturbed sites. It is also one of the major weeds in nurseries. It is a competitive plant in landscaped areas and gardens, but it is generally not a problem in lawns. In addition to the general weediness of this plant, it also can cause chronic liver poisoning to horses, cattle, and swine, even if only a small amount is eaten over a few weeks' time.The success of common groundsel as a weed lies in its seeds. It starts developing seeds very early in its life cycle and can produce 25,000 or more seeds per plant under optimal conditions, although about 1,700 seeds per plant are more likely. These seeds are easily spread by wind. Additionally, there can be three or more generations per year. Even when the plant is pulled from the ground or cut down, seeds from open flowers can still mature and germinate. This weed was also one of the first to have populations develop resistance to some common agricultural herbicides.
