Flowers presenting with a spherical form are often composed of clusters of small flowers, as with alliums, hydrangeas and some varieties of viburnum. Spherically formed flowers provide textural contrast to vertically shaped flowers or horizontally growing foliage in the flowerbed or border. Include ball-shaped flowers of several sizes and seasons for a complete garden design.
The home gardener grows only a few of the more than 500 species of spring or summer blooming ornamental allium. Among these are choices ranging from diminutive flower clusters on 6-inch stems to large flowers on stems 4 feet tall. A. giganteum is from Central Asia. Its 4-foot-tall stems support 10-inch globes of bright lavender flower heads. Protect this plant from winds. A. "Globemaster" has deep violet, 6- to 8-inch globes on 2- to 3-foot stems. A. sphaerocephalum, called the drumstick allium, produces 1.5-inch reddish-purple flower clusters on 2-foot stems, and is drought tolerant. A. karataviense has pink to white, 3-inch flower globes on 6-inch stems.
Summer-blooming agapanthus, commonly called lily of the Nile, or African lily, displays clusters of blue or white flowers in a spherical "burst" at the top of a tall, bare stem. The plant forms large clumps of leaves in a fountain form, from which the bare stems emerge. Agapanthus is for low-frost regions. A. africanus varieties are evergreen, producing flower-topped stalks to 1.5 feet high. "Albus" is white flowering. "Bleu Baby" is light blue. "Summer Gold" has yellow-edged leaves and deep blue flowers.
Hydrangea macroophylla, native to Japan, produces large flower clusters in pink, blue or white, summer through fall. These are the florist's hydrangeas, and are hardy to U.S. Department of Agriculture Plant Hardiness Zone 6. The color of the flowers depends on the soil pH levels and the chosen cultivar. Blue flowers are produced in an acidic soil, and neutral to alkaline soils produce pink. Soil levels between neutral and acidic will produce either purple flowers or pink and blue flowers on the same plant. Some cultivars, such as "Alpengluhen," are non-blueing.
Viburnum macrocephalum is the Chinese snowball bush. Blooming in April, a mature plant can reach 12 to 20 feet tall, covering itself with masses of pure white floral "snowballs." The flower clusters are 6 to 8 inches across. The Japanese snowball bush, Viburnum plicatum, produces smaller, tennis-ball-sized balls of blossoms in May. The Japanese snowball bush "Mariesii" was awarded the Royal Horticultural Society's Award of Garden Merit. Both Chinese and Japanese snowball plants are hardy in USDA zones 5 through 7 and require a moist, well-drained soil in full sun to partial shade.