As with many deciduous shrubs, spring is the best time to plant Korean spice viburnum, as this gives the plant plenty of time to develop a good root system before winter. Like most viburnums, this is a relatively slow grower, adding 1 to 2 feet per year until it reaches its mature size of about 6 feet. Some cultivars are shorter plants, but these are even slower growing, still requiring at least three years to reach their mature size and begin producing flowers. Korean spice shrubs should be planted in rich, well-draining soil at the same height as they are in the nursery pot. Dig a well-prepared hole about twice the diameter of the nursery container, and back-fill with soil amended with plenty of organic matter, such as compost. If planting multiple shrubs, space them 4 to 6 feet apart to ensure good air circulation.
Light
Plant this shrub in full sun or partial shade. A sunnier location will lead to more profuse flowering.
Soil
These bushes grow best in the moist but well-drained soil with a slightly acidic soil pH. They do not do well in very wet soil.
Water
Maintain evenly moist soil with regular watering. Weekly watering—about 1 inch per week—is typical in many areas, but drier climates or seasons may necessitate more frequent watering. This plant is relatively drought-resistant once established but will perform best if it receives a deep weekly watering during dry spells
Temperature and Humidity
Viburnums are generally tolerant of high heat but do best with some shade during the hottest periods of summer. They prefer humid climates, but will tolerate dry conditions.
Fertilizer
Feed the plant in spring with a slow-release tree and shrub fertilizer to support overall health and promote future blooms. Don’t feed late in summer because this can force new growth that can be damaged by fall frost.
Types of Korean Spice Viburnum
Several varieties of Korean spice viburnum are available, some of which are cultivars, others that are crosses between V.carlesiii and other species:
‘Aurora’ is a slower-growing rounded shrub that generally stays around 4 to 5 feet in height.‘Cayuga’ is a very reliable cultivar similar to the species plant. It grows 4 to 10 feet tall and is a very profuse bloomer, producing 4-inch-wide white clusters in spring.‘Compactum’ is a smaller variety of Korean spice viburnum that grows 2 1/2 to 4 feet tall and wide with flowers colored the same as the pure species, white.‘Spice Girl’ is a relatively compact, 6 to 7-foot shrub with flowers that hold a pink color for a considerable length of time before fading to white. It makes an especially good hedge plant due to its dense growth habit. ‘Spice Island’ is 3 to 5 feet tall with white flowers, and dark green leaves with good red fall color.‘Sugar N’ Spice’ is 4 to 5 feet high with dark green leaves that turn maroon-red in fall.Viburnum × carlcephalum is a cross between V. carlesii and V. macrocephalum var. keteleeri. It has large snow-ball-like flowers, and is hardy in zones 6 to 8. It grows 6 to 10 feet tall.Viburnum x burkwoodii (Burkwood vibernum) is a cross between V. utile and V. carlesii. It is a broad, dense shrub reaching 8 to 10 feet, with flat-topped white flowers blooming in April.
Pruning
Korean spice viburnum from their flower buds on old wood—the prior season’s growth. Therefore, if you wish to prune the plants in order to shape them and/or restrict their size, do your pruning just after they have finished flowering. Simply cut the branch tips to promote further branching and a bushier look. Also, remove any dead branches and those that rub against each other.
Propagating Korean Spice Viburnum
The best way to propagate Korean spice viburnums is by taking softwood cuttings in spring as new growth appears. Here’s how to do it: Remember that with trademarked or registered cultivars (such as Spice Girl®), it is illegal to propagate the plants yourself, either vegetatively or by collecting and planting seeds. Doing so can potentially lead to serious legal consequences resulting from copyright infringement.
How to Grow Korean Spice Viburnum From Seed
Growing viburnums from seed is not often done, as the process is lengthy, requiring as much as 18 months before the seeds even germinate and sprout. If you want to try it, collect some seeds from the dried fruits, then store them in a moist, warm environment (76 to 86 degrees Fahrenheit) for about two months. Next, they will need a winter-like period of cold stratification (you can do this in a refrigerator) for three months. Now, the prepared seeds can be sown in seed flats (just barely covered with seed starter mix) until they sprout. When true leaves appear, the tiny seedlings can be transplanted into individual pots and grown on for at least a full season, until they are large enough for garden planting. The entire process can take as many as three years, so it’s much more common to propagate by rooting stem cuttings.
Potting and Repotting Korean Spice Viburnum
Not all viburnums are suitable for container culture, but smaller cultivars of Korean spice viburnum usually do fairly well. Choose a pot that is somewhat larger than the plant’s nursery container (a pot at least 20 inches in diameter is recommended). Because potted viburnum can be sensitive to heat on the roots, choose a material that does not absorb heat, such as a resin pot or one made from fiberglass. Use a potting mix that is slightly acidic and well-draining. A mixture of standard potting soil and perlite or sand works well. A potted viburnum will need more frequent watering and feeding than an in-ground shrub. Plan on watering at least twice a week and feeding monthly. A potted viburnum will quickly use up the soil’s nutrients, so repot it every four or five years. Rather than potting up to a larger container, remove the plant from the pot, shake off the soil, then replant it into the same container using fresh growing mix.
Overwintering
Viburnums are very hardy shrubs that generally do not require winter protection against cold—at least if they are grown within their recognized hardiness range. With all viburnums, withhold water and fertilizer as fall progresses. Avoid allowing the shrub to soak in damp conditions over the winter, as this is an invitation to root rot. A blanket of mulch over the root zone can be helpful if you are growing the shrub in a region where it is borderline hardy. In these regions, some growers protect the shrub with a tent or wrap of burlap for the winter to avoid winter burn. However, viburnums generally recover nicely from some winter dieback.
How to Get Korean Spice Viburnum to Bloom
A mature, healthy Korean spice viburnum will generally reward you with plenty of large flower clusters that last for several weeks sometime in early to late spring. If the flower show disappoints, it’s usually for one of these reasons:
Plant is too young: Korean spice viburnums generally don’t flower until they are at least three years old. If you have planted a young nursery plant—or are propagating one of your own—be patient.Shrub is not getting enough sun: A shrub growing in dense shade will rarely flower robustly, though you should get some flowers.Untimely frost killed buds: If a very hard frost hits in the early spring (or too early in the fall) it can potentially kill off the upcoming season’s flower buds.Soil is too alkaline: Viburnums like a slightly acidic to neutral soil, and if your soil is too alkaline (common in desert or prairie regions), then you may need to feed with an acidifying fertilizer to enjoy good flowering on your viburnum.Pruning has been improper: If the shrub is pruned too late in the year, all the “old wood” that produces flower buds will be removed. Remember that these shrubs should be pruned immediately after they flower, then left alone.The shrub has been fed too much nitrogen: Excessive nitrogen can stimulate plenty of green leaf development but at the expense of flowering. This is common when a viburnum shrub is planted adjacent to lawn areas that are frequently fed with nitrogen-rich fertilizerThe shrub is diseased: A viburnum shrub that struggling due to a pest or disease problem often conserves its energy by flowering less profusely. Manage health issues as they arise.
Common Pests & Plant Diseases
It’s quite likely your Korean spice viburnum will never show any pest or disease problems at all. But one problem you may experience is leaf curl at the tips of branches. The culprit will most likely be aphids. If you can manage to catch them in action, spray them with organic neem oil. Luckily, if restricted to just a relatively small portion of the entire plant, leaf curl does no long-term harm. Prune off the affected branch tips and dispose of them properly, and the plant will be none the worse for it. Korean spice viburnum can also be susceptible to viburnum crown borer, an insect that bores holes in the lower stems, causing die-back. Keeping the plant in good health often prevents these insects from gaining a foothold. Where crown borers are known to be a problem, pesticides sprayed on the lower 12 inches of the stems can kill borers before they damage the shrub. Bacterial leaf spot, powdery mildew, and Armillaria root rot are among the diseases that occasionally cause problems with this plant. Prevent these problems by giving them good air circulation by watering them at ground level, and making sure the soil has excellent drainage. Diseased plant parts should be cut away and discarded.
Common Problems With Korean Spice Viburnum
In most cases, reported complaints with Korean spice viburnum are due to pest problems and fungal diseases that cause leaf spots or branch die-back (see above). But another very common cause of leaves drying up and branches dying back is simply that the plant is suffering the effects of drought. Although this shrub is sometimes described as having good drought resistance, that reputation only holds for well-established plants and for relatively short drought periods, up to four weeks or so. It’s quite common in these days of water-usage sensitivity for homeowners to allow ground-covers and garden plants to get quite thirsty—the belief is that they readily go dormant and will quickly return once rainfall returns.Korean spice viburnum falls into that category of plants that is drought tolerant only up to a certain point. Beyond that line, the shrub will quickly make you pay for your miserly approach to water. It’s best to water your thirsty viburnum deeply and immediately when you begin to see leaves start to dry up and turn black.
