Fleabanes are a group of herbaceous perennials in the Aster family, mainly in the genus Erigeron and a few related genera. Fleabane is one of the best flowers for attracting beneficial wasps as well as bees, butterflies and birds, and it is deer resistant. Propagation is by seed or division.
Philadelphia Fleabane (Erigeron philadelphicus) is a one- to two-foot tall fleabane that is native in the northern and western parts of Davis (and throughout most of the U.S., including Philadelphia). Depending on environmental conditions, it can complete its life cycle as an annual or as a short-lived perennial. It grows along roadsides or in fields, thickets, or sunny woodlands. A single plant can bear as many as 35 flower heads. Philadelphia fleabane has been introduced to much of Europe and Asia, where it is an invasive weed.
Leafy Fleabane (Erigeron foliosus) is a one- to three-foot tall perennial that is native in the Yolo County foothills but not in Davis. It can be planted and grown in Davis, however. It prefers partial shade but can take considerable sun. It has multiple stems branching from the same base, with each stem bearing one or a cluster of a few flower heads at the top.
Mexican Fleabane (Erigeron karvinskianus) is a non-native, semi-evergreen perennial that will go deciduous when hit by hard frost. Erigeron is a large genus of 200 or so species that are widely distributed in grasslands and high mountain areas; E. karvinskianus is native from Mexico to Venezuela but grows so well in the Santa Barbara area that it's adopted Santa Barbara Daisy as one of its names. Other names for this hardy bloomer include Mexican Daisy, Dancing Daisy, Latin American Fleabane, and Seaside Daisy. Whatever you choose to call it, this beautiful little plant produces cascading mounds of delicate little daisy-like flowers virtually year 'round beginning in early spring. Each small, pink bud develops into a white daisy flower with a large yellow center and very narrow "double" petals. A plant typically spreads out about two feet, lazily reaches maybe eight inches in height, and requires little care aside from a little protection from Davis' intense sun and regular summer watering. It seems to do equally well in partial sun or shade and is said to thrive in abandoned gardens, stone walls, or cracks in the sidewalk. A fairly vigorous grower, it can be invasive along the coast, though it is not rated by the California Invasive Plant Council and doesn't seem to be a problem in our Davis climate and clay soil.
Horseweeds are occasionally called fleabanes and are very closely related to the species above. Horseweeds are sometimes classified as part of the same genus (Erigeron) as the species above but other times classified as a separate genus (Conyza). In Davis we have both the native Canada Horseweed/Canada Fleabane (Conyza canadensis) and the non-native Hairy Horseweed/Hairy Fleabane (Conyza bonariensis). Both are common garden weeds and not most people's idea of pretty.