Viburnum Plicatums & Summer
- The doublefile viburnum blooms in mid- to late spring, but in cold winter regions the flowering may be delayed into June around the summer solstice. The Japanese snowball viburnum naturally begins flowering two to three weeks later than the doublefile, according to Michael Dirr, an American woody plant expert. Therefore, it's common that the snowball is in flower in mid- to late June in cold winter regions such as USDA zone 5 around the summer solstice. By mid-June, doublefile viburnums may already be displaying tiny red berries.
- Besides timing of flowering and fruiting, latitude and elevation affects how much sunlight or lack of soil moisture is tolerated by Viburnum plicatum shrubs. For example, in the northern United States, where sunlight intensity and heat are less than in the Deep South, viburnum shrubs tolerate full sun and dry soil better. Since summers are longer, hotter and sunlight more intense in the southern U.S., these plants may more quickly show signs of drought stress when in full sun and sandier soils. Dirr suggests these shrubs should be mulched and sited in partial shade in the South.
- Again, depending on precise flowering time per geography, light pruning of both the doublefile and Japanese snowball viburnum forms needs to occur immediately after flowering ends. In northern regions, pruning occurs in late June to early July. The shrubs are well formed and typically don't need pruning, but any shaping or trimming branch tips needs to be completed quickly once flowering ends. Japanese snowball shrubs produce sterile flowers, so no fruits occur in summer. By contrast, doublefile viburnums do yield ornamental clusters of fruits that gardeners may not want to prune away. Birds certainly harvest the red to black fruits for food in summer. Dirr suggests completing any trimming by August at the very latest.
- Monitor the health and vitality of doublefile and Japanese snowball viburnums across the summer. Dead, broken or diseased branches may be pruned away at any time. Sudden oak death disease is known to infrequently infect both forms of Viburnum plicatum. Another disease to look out for and prune away sickly branches from is Botyryopshaeria canker, which occurs when plants are drought-stressed. Irrigate shrubs in summer to keep them healthy. Don't prune or worry about seasonal bouts with downy mildew or powdery mildew, but rake up the fallen leaves to remove them from the bed. Neither the viburnum beetle nor viburnum borer are worrisome issues with this viburnum species. Hungry deer may browse on the shrubs in some regions.
