Just because they are called snowball bushes doesn't mean that you plant them in winter. "Snowball bushes" are shrubs that produce round clusters of white flowers that look something like snowballs. Many are deciduous shrubs in the viburnum genus, but a certain hydrangea also bears snowy, globular inflorescences in addition to the common-name snowball bush.
Whether you plant viburnum or hydrangea shrubs, you can plant them in the fall. The ideal time for transplanting is while the plants are dormant.
So Many Snowballs, So Little Time
If you want a shrub about your own height that offers bright green leaves and shining, round snowballs of flower clusters, you'll have to use the "eenie meenie miney mo" system for choosing among the many available. You can go with snowball hydrangea or snowball viburnums, depending on which best fits your needs.
Several different hydrangea bushes offer round, tight clusters of white flowers in the shape of snowballs. You can pick Pee Gee hydrangea (Hydrangea paniculata 'Grandiflora') if you live in U.S. Department of Agriculture plant hardiness zones 3 through 8 for a fast-growing shrub that reaches up to 20 feet in each direction. It produces huge white panicles of blossoms that turn purple-pink over the summer and grows in sun or partial shade.
Alternatively, go with smooth hydrangea (Hydrangea arborescens 'Annabelle') in USDA zones 3 through 9. It's better for smaller gardens since it only grows to 5 or 6 feet in each direction but offers enormous clusters of sterile white flowers. Each "snowball" flower can get to 12 inches across. Smooth hydrangea prefers a shady location.
Both of these hydrangeas are deciduous plants, Because they are usually sold as potted plants, they can technically be planted any time of the year. It is best to plant them in early summer or fall, however. Plant them in spring if you live in an area where you don't get freezing temperature in spring. If you are transplanting a hydrangea, do so when the plant is dormant in fall or winter. Avoid transplanting when the ground is under snow or frozen.
Your dream snowball bush might be a viburnum, a large family of ornamental shrubs admired for their bright foliage, generous spring blossoms and fall berries. Several have snowball-like flowers, including Chinese snowball bush (Viburnum macrocephalum 'Sterile' ) and Japanese snowball bush (Viburnum plicatum plicatum) and common snowball bush (Viburnum opulus 'Roseum').
Both Chinese and Japanese snowball bush thrive in USDA zones 5 through 7, and the shrubs look similar. The Chinese snowball is more dramatic, with 8-inch, snowball flowers, and grows to 20 feet tall, while its Japanese cousin only grows to 15 feet with tennis-ball-sized flowers. Both offer green flowers that whiten as they mature.
The European snowball bush is actually a highbush cranberry that grows to about 10 feet high and some 7 feet wide, offering its snowball flowers in May. The cultivar 'Roseum' is sterile, so the bush produces 3-inch round flower clusters but no berries.
It is best to plant viburnums in the fall, when you expect cooler weather and more moisture. But since most viburnums are offered in containers in the springtime, you can also plant them then. Be sure spring-planted viburnums get regular irrigation. If you are transplanting an established viburnum, do so while the plant is dormant, during spring, fall or even winter, in mild regions.