Plant Spiraea thunbergii 'Mellow Yellow(TM)' where you want early-spring sparkle and season-long color. This graceful deciduous shrub opens with tiny white flowers along arching stems, then follows with narrow, willow-like leaves that glow chartreuse to golden yellow and finish with warm fall tones. At maturity it typically reaches about 48-60 inches tall with a similar spread, forming a light, fountain-like silhouette that fits easily into mixed beds and foundation plantings.
Give it full sun for the strongest foliage color, though it will also grow well in part shade. Average, well-drained soil is ideal; once established it handles some drought and is adaptable to a range of soils as long as the site does not stay wet. Use it on slopes, as a low informal hedge, or as a bright contrast against dark evergreens or purple-leaved shrubs.
For best bloom, prune right after flowering, because next spring's flowers form on the previous season's growth. A light thinning of older stems keeps the plant airy and encourages fresh new canes. In cold-winter regions, allow it to go dormant naturally; in spring it leafs out quickly and is ready to shine again. Hardy in USDA Zones 4-8.