Snowball Viburnum is the June 2019 Plant of the Month

June 2019 plant of the month series for Erie and Boulder Colorado area landscapes

June, 2019: Snowball Viburnum

Snowball Viburnum. Viburnum ‘Opulus’ is the sterile species cultivated for the showy large mophead flowers that are abundant in May along the Front Range of Colorado. It is sometimes confused with other mophead Hydrangeas when small, but the Viburnum is a large shrub, growing to 12’ high and wide. Give it plenty of room and the show stopping flowers will dazzle. It tolerates a wide range of soils, needs adequate moisture to become established, but does not need an abundance of water. It prefers some winter shelter, as do most plants in the harsh Colorado climate. It prefers some shade from the afternoon heat, but can tolerate direct sun most of the day. A bit of fertilizer each spring before it blooms will help aid the plethora of large flowers. Prune in summer after flowering to maintain shape.

There are some downsides to the plant in Colorado, but the blooms in spring are worth the troubles. It can be susceptible to aphids. It is frequently injured by the early spring leaf and twig-curling snowball aphid Ceruraphis viburnicola. Twisted, curled, distorted, cupped foliage is the primary symptom. Severely infested plants may also have the branches bent and twisted like a corkscrew. The feeding of the aphids causes the foliage to be distorted and, when numerous, these aphids stunt the early growth of the Viburnum completely. They can be controlled by applying neem oil in March. Natural biological controls are a first step. Ladybugs and Green Lacewing can be purchased locally to release onto the shrub in spring and they will do a great job of controlling minor infestations. Major infestations sometimes occur in moist spring conditions and may require insecticidal soap which does not leave a chemical residue, or malathion or permethrin for severe conditions. A well maintained landscape with an abundance and diversity of predatory insects is usually sufficient to keep Viburnum aphids at bay.

In its native form, Snowball Viburnum will have berries, but the ‘Opulus’ cultivar planted in landscapes is sterile. The native form is sometimes confused with or labeled as a Cranberry, but it is not. It is one of the national symbols of Russia, has some interesting Ukrainian folklore associated with it, and a picture of the berry cluster from the non-sterile version is the insignia of the Ukrainian Army. The berries symbolize ones family roots, or bloodline, and home. It is even depicted in certain Slavic paganism stories, symbolizing the beauty of a young lady.

Plant one in an open space of your Erie Colorado landscape, giving it plenty of room to flourish, and enjoy the massive blooms for years to come. If there is room, plant several as a hedgerow for privacy. They do not disappoint.

Contact Dave to learn about a free consultation and estimate for your local Broomfield (Boulder), Colorado area landscape project. Follow us on Pinterest or Facebook to see our featured landscaping project photos