Botanical Classification
The Smoke Tree, scientifically known as Cotinus coggygria, is a deciduous shrub or small tree in the Anacardiaceae family, which includes sumacs, poison ivy, and cashews. Its botanical classification places it in the genus Cotinus, closely related to Rhus, with the synonym Rhus cotinus sometimes used.
The species name coggygria reflects its historical use as a source of yellow dye, derived from the Greek words for “smoke” and “wild olive,” alluding to its smoky flower plumes and leaf shape. This plant is valued for its ornamental qualities, particularly its vibrant foliage and unique, wispy flower clusters, making it a popular choice in landscaping.
Native Area And Distribution
Native to southern Europe, the Mediterranean region, and central China, Cotinus coggygria is found from Italy and France through the Balkans, Turkey, the Caucasus, and into the Himalayas and northern China. It thrives in rocky hillsides, open woodlands, and scrublands, often on well-drained, infertile soils.
Introduced to North America as an ornamental by 1656 and widely available in nurseries by 1790, it has become a staple in temperate gardens worldwide. Distinct from the native American smoketree (Cotinus obovatus), which grows in the southeastern United States, C. coggygria is more common in cultivation due to its showy cultivars and adaptability.
History
Historically, the Smoke Tree has been valued for both aesthetic and practical purposes. In its native range, its wood and leaves were used to produce a yellow dye, earning it the name “dyer’s sumach,” particularly in Europe during the medieval and early modern periods. Its ornamental appeal drove its spread to Western gardens, with cultivars like ‘Royal Purple’ and ‘Velvet Cloak’ developed for their striking purple foliage.
These cultivars, along with its low maintenance and vibrant seasonal displays, have made it a favorite in English and American gardens since the 16th century, appreciated for its ability to thrive in diverse conditions.
USDA Zones
The Smoke Tree is hardy in USDA Zones 5a to 8b, tolerating temperatures as low as -20°F (-29°C), making it suitable for much of the United States, Europe, and temperate Asia. It thrives in full sun to ensure vibrant foliage and optimal flowering but can tolerate partial shade, though this may cause purple-leaved varieties to revert to green.
The plant prefers well-drained, somewhat infertile loams with a pH range of 3.7 to 6.8, adapting to rocky, sandy, or clay soils. Its drought tolerance and ability to grow in poor soils enhance its versatility, though it dislikes waterlogged conditions.
Identifying Characteristics
Cotinus coggygria typically grows 10-15 feet tall and wide, occasionally reaching 23 feet, with an open, spreading, irregular habit, though it can be trained into a small tree. Its leaves are simple, alternate, oval, 1.25-3.25 inches long, with a waxy, glaucous sheen, green in the species but deep purple in cultivars like ‘Royal Purple.’
Fall foliage ranges from peach and yellow to scarlet or reddish-purple, providing vivid seasonal color. The tree’s hallmark is its large, airy panicles (6-12 inches long) of tiny, yellowish flowers in mid-summer (June-July), most of which abort, leaving pinkish-purple or yellowish feathery plumes that create a smoky effect, hence the name.
The fruit is a small, kidney-shaped drupe, inconspicuous and rarely noticed. The bark is smooth, light gray to brown, becoming flaky with age, and the sap, which may cause contact dermatitis, has a radish-like scent when leaves are crushed.
Landscape Uses
Specimen Plant
- Acts as a striking focal point in gardens or lawns due to its vibrant purple or green foliage, smoky flower plumes, and vivid fall colors.
- Ideal for small to medium landscapes, given its moderate size (10-15 feet tall and wide).
Shrub Borders and Mixed Plantings
- Enhances mixed borders with its bold foliage, pairing well with shrubs like hydrangeas, spirea, or perennials such as yarrow and salvia.
- Purple cultivars (e.g., ‘Royal Purple’) contrast beautifully with green or golden plants, adding depth and texture.
Informal Hedges or Mass Plantings
- Suitable for informal hedges or grouped plantings to create a colorful, textured screen or backdrop.
- Provides a cohesive look when planted in rows, especially with consistent cultivars for uniform foliage color.
Urban and Low-Maintenance Gardens
- Tolerates urban pollution, drought, and poor soils, making it ideal for city parks, streetscapes, or low-maintenance landscapes.
- Fits well in xeriscapes or sustainable gardens due to its water-wise nature once established.
Seasonal Interest
- Spring/Summer: Lush foliage and smoky pinkish-purple or yellowish plumes (June-July); Fall: Brilliant red, orange, or purple leaves; Winter: Sculptural branching.
- Flower plumes add a unique, airy texture, persisting into late summer.
Wildlife and Pollinator Appeal
- Flowers attract bees and butterflies, supporting pollinator-friendly gardens.
- Minimal wildlife damage, as it is generally unpalatable to deer and rabbits.
Ornamental Accents
- Dried flower plumes used in floral arrangements for indoor decor, adding a soft, smoky effect.
- Purple foliage cultivars serve as strong accent plants against lighter backgrounds.
Versatile Forms
- Can be maintained as a multi-stemmed shrub or pruned into a small tree, offering flexibility for various design needs.
- Compact cultivars (e.g., ‘Young Lady’) suit smaller gardens or containers.
Challenges
- Sap may cause contact dermatitis in sensitive individuals; avoid planting near high-traffic areas for those with allergies.
- Flower plumes and leaves may create light litter, requiring occasional cleanup in formal settings.
Cultivation of Smoketree
Site Requirements
- Light: Full sun (6+ hours daily) for optimal foliage color and flower plume production; tolerates partial shade, but purple cultivars may revert to green.
- Soil: Well-drained, prefers infertile loams; adapts to clay, sandy, or rocky soils; pH 3.7-6.8; dislikes waterlogged conditions.
- Hardiness: USDA Zones 5a-8b, tolerating temperatures to -20°F (-29°C).
Planting
- Plant in spring or fall, spacing 10-15 feet apart to allow for mature spread; dig a hole twice as wide and as deep as the root ball.
- Incorporate minimal organic matter in poor soils; avoid overly rich soils to maintain vibrant foliage color.
- Apply 2 inches of mulch (e.g., bark or gravel), keeping it 2 inches from the trunk to prevent rot.
Watering
- Water deeply weekly during the first 1-2 years to establish roots; reduce to minimal watering once established, as it is highly drought-tolerant.
- Avoid overwatering, especially in clay soils, to prevent root rot; ensure proper drainage.
Fertilization
- Minimal needs; apply a balanced, slow-release fertilizer (e.g., 10-10-10) in early spring only if growth is poor or soil is deficient.
- Avoid high-nitrogen fertilizers, which can reduce foliage color intensity and weaken structure.
Pruning
- Light Pruning: Early spring, remove dead, damaged, or crossing branches to maintain shape and promote blooms (flowers form on old wood).
- Hard Pruning: Late winter, cut back to 6-8 inches above ground for rejuvenation; encourages lush foliage but may reduce flowering that season.
- Tree Form: Prune to a single leader, removing lower branches gradually; remove suckers at the base for tidiness.
- Wear gloves to avoid sap irritation; disinfect tools to prevent disease spread.
Pests and Diseases
- Generally pest-resistant; occasional issues include scale, spider mites, or aphids, treatable with horticultural oil or insecticidal soap.
- Susceptible to leaf spot, rust, or verticillium wilt in humid or poorly drained conditions; improve air circulation and drainage to minimize.
- Root rot possible in wet soils; select well-drained sites and avoid overwatering.
Propagation
- Cuttings: Take 4-6 inch semi-hardwood or softwood cuttings in late spring/early summer; dip in rooting hormone, plant in well-draining mix, keep moist.
- Seeds: Collect seeds in fall, sow in spring after cold stratification; germination is slow and unreliable due to high infertility.
- Suckers: Dig up root suckers in spring for transplanting, though less common for cultivars.
Maintenance Tips
- Monitor for suckers or unwanted seedlings, especially in fertile soils, to maintain desired form.
- Rake up fallen leaves or plumes in formal landscapes to keep tidy.
- Inspect for storm-damaged branches, as wood can be brittle; prune promptly to prevent further damage.
- Tolerates urban pollution, drought, and poor soils, making it low-maintenance once established.
Challenges
- Purple cultivars may fade to green in shade; ensure full sun for best color.
- Sap can cause skin irritation; handle with care during pruning or maintenance.
- Avoid planting in low-lying areas prone to water pooling to prevent root issues.
- May not bloom profusely in cooler climates or after heavy pruning.