Spiraeas

Spiraeas are deciduous shrubs of the genus Spiraea in the family Rosaceae. With roughly 80 to 100 species, they are widely cultivated as ornamental plants and are commonly known as spireas. Native to temperate regions of the Northern Hemisphere, they are especially common in Asia and Europe, with several species naturalized in North America.

They range from about 0.5 to 3 meters in height, with arching branches and dense, twiggy growth. Leaves are usually small, simple, oval to lanceolate with serrated margins. Flowers form in dense clusters at the ends of shoots and are typically white, pink, or occasionally yellowish. Bloom time ranges from late spring to early summer, and some cultivars rebloom.

In cultivation they prefer full sun and well-drained soil; they tolerate a range of soil types and are relatively drought-tolerant once established. They are hardy in many climates, though exact hardiness depends on species. Pruning is often recommended after flowering, because many spiraeas set fruit or buds on old wood; some cultivars flower on new growth, in which case pruning timing may differ.

They are widely used in borders, as specimen plants, hedges, or for erosion control on slopes. Notable species and cultivars include Spiraea japonica (Japanese spirea) with many cultivars such as 'Goldmound' and 'Little Princess', Spiraea x vanhouttei (Vanhoutte spirea), Spiraea cantoniensis, and Spiraea douglasii (Douglas spirea).

Pests and diseases include fire blight, powdery mildew, and leaf spots; good air circulation and proper watering reduce problems. Some species can naturalize beyond cultivation, and in some regions may spread aggressively.