The Clethra ‘Vanilla Spice’ that began as a garden trial four years ago has matured into a lovely, medium-sized shrub. While not easily found at retailers, this is a highly desirable shrub well worth locating and planting.
This cultivar grows well in acidic or alkaline soil. The natural environment for Clethras is woody swampland, so they all require constantly moist soil; however, once established, an inch of rainfall per week is adequate to grow ‘Vanilla Spice’. If weekly rainfall is unreliable, choose a location with easy access to supplemental watering.
Established plants can tolerate up to ten days without water when temperatures are moderate. Young plants are much more moisture sensitive: if not planted in a naturally damp site, moisture-retaining crystals should be added to the soil when first planting.
Providing the right amount of sunlight requires a balance with soil moisture. In regularly damp soil, ‘Vanilla Spice’ grows well in full sunlight. In the absence of damp soil, locate the plant either where it receives morning sun, very light shade or under very tall trees. Otherwise you may be constantly supplying extra water to keep the plant healthy.
Aesthetically, ‘Vanilla Spice’ can be used as a specimen, low hedge or within a mixed border. Bees are active when the shrub is in bloom, so best not to plant too close to entry doors.
Fairly slow growing the first two years, Clethra ‘Vanilla Spice’ develops well in the third and fourth seasons. In 2010, I planted a 9″ (23 cm) tall container-grown shrub from a one-gallon pot. By 2014, the plant reached its mature size of 42″ (107 cm) high by 42″ (107 cm) wide. In a slightly sunnier location, I suspect the ultimate height would be 48″ (122 cm). Clethras grow by rhizomes, so if suckers develop, clip them off at ground level.
This is a gracious, refined shrub with leaves and flowers superior to the species. Leaves are a shiny, medium green that turn a pleasant shade of yellow in the fall. Branches grow to the ground on an open, vase-shaped plant.
Flowers are a pure white bottlebrush shape, unlike the pointed flowers of the species Clethra. Their fragrance is a light, spicy vanilla–just as the name suggests. It is a reliably prolific bloomer each August.
Clethra ‘Vanilla Spice’ is certainly hardy to Zone 4. Although my shrub isn’t totally exposed to prevailing westerly winds, it withstood last winter’s brutally low temperatures with no damage or dieback. On the whole, ‘Vanilla Spice’ is a much easier and more reliable cultivar to grow in Zone 5 than the smaller Clethras such as ‘Hummingbird’ or ‘Sixteen Candles’. This plant is very late to leaf out in the spring, so don’t look for winterkill until late May.
I haven’t observed any leaf fungus, cankers or blights.
Last year, a few leaves were damaged by a mystery chewing insect. Otherwise, this shrub isn’t bothered by insect pests.
Pruning and Fertilization
No pruning is required other than for possible suckers. If desired for aesthetic reasons, the plant can be pruned back by 20% after flowering. I typically apply a low-ratio, slow-release fertilizer early in the season, although Clethras don’t require fertilizer so much as the correct amount of sun and water.