Shirobana Spirea (Spiraea japonica c.v. Shirobana) is a dwarf Japanese spiraea cultivar that grows to be 2 to 3 feet tall, with a similar spread. A member of the rose family, the shrub produces bright green, deciduous leaves topped with clusters of white, red and pink flowers. The plant is tolerant of a wide range of care conditions.
Japanese spiraea is native to Japan, Korea and China, though it has naturalised throughout much of North America, including New England and parts of the Midwest. The plant can be found growing in moist conditions, thriving along stream beds. Shirobana spiraea is a suitable landscape plant for U.S. Department of Agriculture planting zones 4 to 9, where it will look its best in full sunlight. Plants grown in partial shade will produce fewer flowers.
Shirobana spiraea is tolerant of a wide range of soils, though it prefers a rich loam. Plants grown in alkaline soils may develop chlorosis, a nutrient deficiency that results in yellowing leaves. Enhance the soil with organic matter, such as compost, and mulch heavily to retain soil moisture, prevent weeds and increase overall plant health. Water freely throughout the growing season, though not enough to cause the soil to become waterlogged. Shirobana spiraea is not drought tolerant.
Feed Shirobana annually in the spring, before new growth emerges. Use a general-purpose fertiliser to promote healthy foliage and flowering. Shear as desired in the summer, after flowers have finished for the season. Japanese spiraea is easy to propagate by cuttings, seed or root division. Hardwood cuttings may be rooted in the fall, while softwood cuttings do best in the summer. The plant transplants with little difficulty as well. Divide plants in the fall for best results.
Spiraea aphids may attack the plant, causing leaf curl and distortion, as well as a sticky residue called honey dew. Treatment is not usually necessary, as rains may wash away the pests, and predatory insects frequently take care of the problem. Most diseases and pests are not serious enough to significantly lower the health of the plant. Avoid watering from overhead, as wet leaves are more susceptible to leaf spot and other fungal problems.