Plant of the Week: Summer Snowflake

The University of Arkansas System Division of Agriculture does not promote, support or recommend plants featured in “Plant of the Week.” Please consult your local Extension office for plants suitable for your region.

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Summer Snowflake
Latin: Viburnum plicatum var. tomentosum

As gardeners, we tend to be greedy. We want plants that have it all: good looks, lots of flowers, easy to grow and freedom from pests.

To help achieve that goal, the Arkansas Green Industry and horticulturists at the University of Arkansas Cooperative Extension Service have teamed up to create the Arkansas Select program. Plants named as Arkansas Select winners are relatively new items that we think provide gardeners with the kind of positive gardening experience they are seeking.

One of the plants designated an Arkansas Select winner for 2004 is Summer Snowflake Viburnum, a selection of the doublefile viburnum known officially as Viburnum plicatum var. tomentosum. The doublefile viburnum is so named because it blooms in clusters along the horizontal stems, with a row of blossoms on each side of the stem, creating a double row.

This Japanese species is one of the most popular of the many viburnums in cultivation. In the typical cultivar, the plant is as broad as it is tall with the limbs arranged in horizontal layers. But in ‘Summer Snowflake,’ a selection released from the University of British Columbia Botanic Garden, the plant is decidedly tall and skinny. It can grow as tall as 15 feet but with a spread of only 6 feet.

Most consider viburnums to be “shrubs,” but they are on the large end of the shrub range or the runtish end for trees. This plant is deciduous with leaves a bright, mid-green color with a pleated appearance. Fall color is a rusty red and quite handsome.

Summer Snowflake first blooms around the end of April or the first of May, about a week after dogwoods finish. The white flowers are individually about the size of a quarter, but borne in a flat head that is to four inches across. The blooms splayed on the horizontal branches give the plants a wedding-cake kind of look when they appear.

Other than the upright growth form, the other thing that sets Summer Snowflake apart from other viburnums is that it is a repeat bloomer. Admittedly, the first bloom of the season is much more showy than the ones to follow, but about once a month, additional blooms pop out here and there on the ends of new growth.

Gardeners favor viburnums because they have multiple seasons of interest; showy flowers, bright red berries and good fall color. Summer Snowflake has two of the three – usually it sets few berries. Part of the reason for its ability to continue flowering during the growing season is because it does not have a load of berries to support.

The upright growth form and repeat blooming habit makes Summer Snowflake an ideal plant for use near an entryway. It could be used near the entry to the home or beside the garden gate in the kind of location where you might use a Japanese maple or dogwood. In addition, the tall, narrow form of the shrub makes it ideal for an informal screen that would not have to be pruned.

Summer Snowflake, like most viburnums, grows best in sunny locations with good garden loam. But it is not overly picky about its growing conditions. It will grow and flower in semi-shade; areas too shady for bermudagrass to grow but where shade tolerant grasses would be expected to survive. It has good drought tolerance once established, but plants in droughty locations will have few repeat blooms. It does not seem bothered by insect or disease problems.

By: Gerald Klingaman, retired
Extension Horticulturist – Ornamentals
Extension News – May 21, 2004

The University of Arkansas Division of Agriculture does not maintain lists of retail outlets where these plants can be purchased. Please check your local nursery or other retail outlets to ask about the availability of these plants for your growing area.

Viburnum plicatum f. tomentosum ‘Summer Snowflake’ (Japanese snowball ‘Summer Snowflake’)

Botanical name

Viburnum plicatum f. tomentosum ‘Summer Snowflake’

Other names

Japanese snowball ‘Summer Snowflake’, Viburnum plicatum ‘Summer Snowflake’, Doublefile viburnum ‘Summer Snowflake’, Viburnum plicatum var. tomentosum ‘Fujisanensis’

Genus

Viburnum Viburnum

Variety or Cultivar

‘Summer Snowflake’ _ ‘Summer Snowflake’ is an upright to open, deciduous shrub with ovate, deeply veined, dark green leaves that turn red-purple in autumn, flat, lacecap-like clusters of creamy-white flowers in late spring and, occasionally, red berries that turn black as they mature.

Native to

Garden origin

Foliage

Deciduous

Habit

Spreading

Toxicity

Berries may cause stomach discomfort.

Awards

RHS AGM (Award of Garden Merit)

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Colour

Flower

White in Spring

Dark-green in Spring; Dark-green in Summer; Red, Purple in Autumn

How to care

Watch out for

Pests

Generally pest-free.

Specific diseases

Leaf spot

General care

Pruning

Pruning Group 8. Tolerates hard pruning.

Propagation methods

Softwood cuttings

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Where to grow

Viburnum plicatum f. tomentosum ‘Summer Snowflake’ (Japanese snowball ‘Summer Snowflake’) will reach a height of 3m and a spread of 6m after 10-20 years.

Suggested uses

Beds and borders, City, Cottage/Informal

Cultivation

Grow in humus-rich, moderately fertile, well-drained or moist but well-drained soil in sun or partial shade.

Soil type

Chalky, Clay, Loamy, Sandy (will tolerate most soil types)

Soil drainage

Moist but well-drained, Well-drained

Soil pH

Acid, Neutral

Light

Partial Shade, Full Sun

Aspect

North, South, East, West

Exposure

Exposed, Sheltered

UK hardiness Note: We are working to update our ratings. Thanks for your patience.

Hardy (H4)

USDA zones

Zone 9, Zone 8, Zone 7, Zone 6, Zone 5

Defra’s Risk register #1

Plant name

Viburnum plicatum f. tomentosum ‘Summer Snowflake’ (Japanese snowball ‘Summer Snowflake’)

Common pest name

Ramorum leaf blight; Ramorum shoot dieback; Rhododendron twig blight; Sudden oak death

Scientific pest name

Phytophthora ramorum

Type

Oomycete

Current status in UK

Present (Limited)

Likelihood to spread in UK (1 is very low – 5 is very high)

Impact (1 is very low – 5 is very high)

General biosecurity comments

Pathogen of larch and other hosts subject to EU emergency legislation. A containment strategy is in place in the UK; reflecting its presence in wider environment/forestry settings in some areas. EU regulatory status is under review.

Defra’s Risk register #2

Viburnum plicatum f. tomentosum ‘Summer Snowflake’ (Japanese snowball ‘Summer Snowflake’)

assam thrips; castor thrips; chilli thrips; yellow tea thrips

Scirtothrips dorsalis

Insect

Absent

Likelihood to spread to UK (1 is very low – 5 is very high)

EU listed pest for citrus but highly polyphagous and intercepted on a number of hosts. EU legislation should be updated to reflect wider host list.

Defra’s Risk register #3

Viburnum plicatum f. tomentosum ‘Summer Snowflake’ (Japanese snowball ‘Summer Snowflake’)

pink wax scale; red was scale; ruby wax scale

Ceroplastes rubens

Insect

Absent

Based on its biology and low potential impact continued action on this pest in the UK would not be considered appropriate. It is likely to be of more concern to southern Member States of the EU; as it is an economic pest of citrus.

About this section

Our plants are under greater threat than ever before. There is increasing movement of plants and other material traded from an increasing variety of sources. This increases the chances of exotic pests arriving with imported goods and travellers, as well as by natural means. Shoot is working with Defra to help members to do their part in preventing the introduction and spread of invasive risks.

Traveling or importing plants? Please read “Don’t risk it” advice here

Suspected outbreak?

Date updated: 7th March 2019 For more information visit: https://planthealthportal.defra.gov.uk/

Viburnum “Summer Snowflake” (Photo by Brendan Zwelling)

One of the benefits of taking down a large tree in the front garden has been the increased sunlight for plants growing in the area. Everything is bigger and blooming with more flowers! One shrub that’s enjoying more sun is ‘Summer Snowflake’ viburnum (Viburnum plicatum f. tomentosum ‘Summer Snowflake’, Zone 6, 5 x 4 feet / 1.5 x 1.2 m). This is a doublefile viburnum, meaning it has two opposing lines of white flowers marching along its layered, pagoda-style branches. ‘Summer Snowflake’ is more upright and compact than other doublefile viburnums, such as ‘Lanarth’, ‘Mariesii’ and ‘Shasta’. It fits into small gardens, and is a good partner in mixed borders with perennials. ‘Summer Snowflake’ provides a constant show of white flowers, and works as a foil to brighter and darker perennials blooming sequentially through summer.

Aside from its smaller size, ‘Summer Snowflake’ is similar to other doublefile viburnums in almost every respect. It has the same layered form, abundant flowers, drupes of red fruits turning to black (relished by birds), and reddish to bronze-purple fall colour. But it has one great advantage: an ability to produce flushes of flowers from May through October. I’ve experimented with the amount of light necessary to sustain a long season of flowering, and it’s no surprise that the more direct sunlight this shrub gets, the better it blooms. In light shade, it carries only a handful of flowers at any time, however, in four to six hours of sun the shrub blooms generously most of the growing season. Placed in full sun, I’m sure it would be luxuriant with bursts of flowers through the summer.

My only hesitation about ‘Summer Snowflake’ is its borderline cold hardiness, although that isn’t currently a problem. My first shrub was planted about 12 years ago, in the bad old days when my Zone 6a garden would sometimes fall under a temporary cold snap and be more like Zone 5b. That shrub died in a winter cold spell that dipped below normal limits. My garden is warmer now, and borderline hardy plants that once perished here — fragrant winterhazel (Corylopsis glabrescens, Zone 6), to name one — are now surviving and have become well established.

The first doublefile viburnum was procured from a Shanghai garden in 1850 by Robert Fortune, one of the adventurous 19th-century plant hunters. Doublefile viburnums are known for their abundance of bloom, often smothered in flowers when at their peak. Most flowering shrubs bloom three to six weeks, and bloom time can be lengthened in a cool spring or shortened by sudden heat. But ‘Summer Snowflake’ just keeps on flowering regardless of temperature, and gives much pleasure while maintaining a reasonable size. I have two in the front garden, and this year they’re enjoying more light than ever before. And I’m enjoying more flowers!

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