Well-known yellow-flowering shrubs include forsythia and honeysuckle, but many others exist. Before attempting to identify your flowering shrub, eliminate any that you know don't grow in your area. For example, papaya, gold angel's trumpets and compact barberry grow in warm climates only. Consult neighbors and even the local botanical garden to identify yellow flowering shrubs common in your area. Look in gardening books for photographs of shrubs that match yours to positively identify that mystery bush.
Consider the time of year the shrub blooms. Forsythia and spice bush bloom in early spring, before other shrubs show any new growth. Honeysuckle, potentilla and Scotch broom flower all summer long. Witch hazel blooms in mid-to-late winter.
Inspect the bark of the shrub for any unusual characteristics. St. John's Wort has flaking, reddish-brown leaves.
Consider the size of the shrub. Potentilla, compact coral barberry, and St. John's Wort all grow to between 3 and 5 feet tall. Scotch broom, forsythia, Spice bush, honeysuckle and rhododendron grow 6-to-8 feet tall.
Examine the flowers of the shrub. Some shrubs such as forsythia and Scotch broom produce flowers in clusters or spears. Potentilla and spice bush produce tiny individual flowers. Rhododendron, papaya, hibiscus and Gold angel's trumpets produce large showy flowers.
Smell the blossoms. Rhododendron and honeysuckle are known for fragrant blooms. Gold angel's trumpets are fragrant at night.
Inspect the shrub's leaves for interesting details. Some rhododendron have slightly hairy leaves. St. John's Wort has linear, blue-green leaves. Papaya has leaves that grow 2 feet wide.
Watch for fruit in the fall. Spice bush produces crimson berries, while St. John's Wort produces small fruit capsules that persist through winter.