Forsythias are a genus of deciduous flowering shrubs that belong to the olive family. These low-maintenance, fast-growing shrubs feature an upright, arching form and are known for their long branches that fill with brilliant yellow blooms early in the spring. The flowers precede their leaves, which means you get a good look at the blooms with no foliage to block your view. Forsythias are fast-growing shrubs that can add as many as 24 inches in a year, especially the larger varieties. They are best planted in late fall or early spring while the plants are still dormant, but gardeners in frost-free climates can plant them in winter, as well.