Culture Notes
Japanese Snowball grows well in sun to partial shade and any moist soil. The plant transplants well, has a moderate growth rate and grows to a mature height and spread of 8 to 10 feet in many landscapes, but can get larger, especially in spread. The white flowers occur in ball-shaped clusters produced in late spring. Foliage takes on a dark maroon color in September and October.
In contrast to the var. tomentosum, flowers hang from the branches in a more-or-less random fashion.
Planting and establishing shrubs
The most common cause of young plant failure is planting too deep. Plant the root ball no deeper than it was in the nursery. In most instances, the root flare zone (point where the top-most root in the root ball originates from the trunk) should be located just above the landscape soil surface. Sometimes plants come from the nursery with soil over the root flare. If there is soil over this area, scrape it off. The planting hole should be at least twice the width of the root ball, preferably wider. In all but exceptional circumstances where the soil is very poor, there is no need to incorporate anything into the backfill soil except the loosened soil that came out of the planting hole. Never place ANY soil over the root ball. If a row or grouping of plants is to be installed, excavating or loosening the soil in the entire bed and incorporating organic matter enhances root growth and establishment rate.
Weed suppression during establishment is essential. Apply a 3-inch thick layer of mulch around the plant to help control weed growth. Keep it at least 10 inches from the trunk. If you apply it over the root ball, apply only a one or two inch layer.  This allows rainwater and air to easily enter the root ball and keeps the trunk dry. Placing mulch against the trunk or applying too thick a layer above the root ball can kill the plant by oxygen starvation, death of bark, stem and root diseases, prevention of hardening off for winter, vole and other rodent damage to the trunk, keeping soil too wet, or repelling water. Regular irrigation through the first growing season after planting encourages rapid root growth, which is essential for quick plant establishment.
Pests, Diseases and Damaging Agents
Pests: Viburnum aphid is gray to dark green and feeds in clusters at the tips of the branches, causing leaf curl. Tarnished plant bug causes brown spots on the flowers and young shoots. Treehoppers lay eggs under the bark, then cover them with a white, sticky substance. Inspect the stems of unhealthy-looking plants for possible scale infestations. The viburnum beetle (Pyrrhalta viburni) causes defoliation, die-back and death of viburnums, however this viburnum is partially resistant to damage from this insect pest.
Diseases: Bacterial leafspot causes round, water-soaked spots on leaves and young stems. Bacterial crown gall forms galls on the lower stems. Do not replant in the same spot. Shoot blight causes grayish to brown decayed spots on the leaves. A number of fungi cause leaf spots. Powdery mildew causes a white powdery growth on the leaves.Â