Botanical classification
The Smoke Tree, scientifically known as Cotinus coggygria, is a deciduous shrub or small tree in the Anacardiaceae family, which also includes sumacs and poison ivy. Its botanical classification places it in the genus Cotinus, closely related to Rhus, and it is sometimes referred to by its synonym Rhus cotinus.
The plant is characterized by its multi-stemmed growth and distinctive fluffy flower clusters, earning it common names like smokebush, European smoketree, or dyer’s sumach. Its taxonomic placement reflects its shared traits with other Anacardiaceae members, such as resinous sap that can cause skin irritation in sensitive individuals.
Native area and distribution
Native to southern Europe and central China, Cotinus coggygria thrives in a range from the Mediterranean through the Caucasus to the Himalayas. Its natural habitat includes rocky hillsides, open woodlands, and scrublands, often on well-drained, infertile soils. Introduced to North America as an ornamental as early as 1656, it became widely available in nurseries by 1790, valued for its striking foliage and unique blooms.
Today, it is cultivated globally in temperate regions, though it is distinct from the native American smoketree (Cotinus obovatus), which grows in the southeastern United States. Its adaptability has made it a staple in ornamental horticulture across diverse climates.
History
Historically, Cotinus coggygria has been prized for both practical and aesthetic purposes. In its native range, it was used as a source of yellow dye, particularly for textiles, which led to its moniker “dyer’s sumach.” Its introduction to Western gardens capitalized on its ornamental qualities, with cultivars like ‘Royal Purple’ and ‘Velvet Cloak’ developed for their vibrant foliage.
The plant’s long history in cultivation reflects its ease of growth and visual appeal, making it a favorite among gardeners and landscapers. Its resilience and low maintenance needs further cemented its popularity in European and North American gardens by the 19th century.
USDA Zones
The Smoke Tree is hardy in USDA Zones 4a to 8b, tolerating temperatures as low as -15°C (5°F). This broad hardiness range makes it suitable for much of the United States, the United Kingdom, and similar temperate regions. It thrives in full sun but can tolerate partial shade, though shade may cause purple-leaved varieties to revert to green.
The plant prefers well-drained, somewhat infertile loams but adapts to a wide range of soil types, including clay, sandy, or rocky soils, and pH levels from 3.7 to 6.3. Its drought tolerance and ability to grow in poor soils enhance its versatility across various climates.
Identifying Characteristics
Growth Habit
- Deciduous shrub or small tree, typically 10-15 feet tall and wide, occasionally reaching 20-23 feet.
- Open, spreading, irregular form, often multi-stemmed; can be trained as a single-trunk tree.
Foliage
- Simple, alternate, oval leaves, 1.25-3.25 inches long, with a waxy, glaucous sheen.
- Green in the species; cultivars like ‘Royal Purple’ or ‘Velvet Cloak’ have deep purple leaves.
- Fall color: vibrant red, orange, or purple, especially vivid in full sun.
- Crushed leaves emit a radish-like odor.
Flowers
- Large, airy panicles (6-12 inches long) of tiny, yellowish flowers, blooming mid-summer (June-July).
- Most flowers abort, leaving hairy, pinkish-purple or yellowish plumes creating a “smoky” effect.
Fruit
- Small, kidney-shaped drupes, inconspicuous, rarely noticed in ornamental settings.
Bark and Stems
- Smooth, light gray bark when young, becoming flaky and textured with age.
- Sap is resinous, potentially irritating to skin and eyes in sensitive individuals.
Distinctive Feature
- Smoky, cloud-like flower plumes, persisting into late summer, give the plant its name.
Landscape Uses
Specimen Plant
- Striking standalone feature due to vivid foliage, smoky blooms, and vibrant fall color.
- Ideal for focal points in lawns, courtyards, or garden beds.
Group Plantings
- Effective in mass plantings or informal hedges for bold color and texture contrast.
- Combines well with plants like hydrangeas, mock orange, yarrow, or ornamental grasses.
Shrub Borders
- Adds structure and seasonal interest to mixed borders, especially with purple-leaved cultivars.
- Complements green or golden foliage plants for visual contrast.
Urban and Specialty Gardens
- Tolerates urban pollution, making it suitable for city landscapes or street plantings.
- Attractive in children’s gardens (non-toxic, though sap may irritate) and butterfly gardens (attracts pollinators).
Seasonal Interest
- Spring/summer: lush foliage and smoky blooms; fall: brilliant leaf colors; winter: sculptural branches.
Decorative Uses
- Dried flower plumes used in floral arrangements for indoor decor.
Versatile Forms
- Can be maintained as a multi-stemmed shrub or pruned into a small tree for varied design needs.
Cultivation of Smoketree
Site Requirements
- Light: Full sun (6+ hours daily) for best foliage color and bloom production; tolerates partial shade (may cause purple leaves to revert to green).
- Soil: Well-drained, prefers infertile loams; adapts to clay, sandy, or rocky soils; pH 3.7-6.3.
- Hardiness: USDA Zones 4a-8b, tolerating temperatures to -15°C (5°F).
Planting
- Plant in spring or fall, spacing 10-15 feet apart to allow for spread.
- Dig a hole twice as wide as the root ball, same depth; avoid low-lying, waterlogged areas.
- Mulch 2 inches deep, keeping mulch 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 (drought-tolerant).
- Avoid overwatering to prevent root rot, especially in heavy clay soils.
Pruning
- Light Pruning: Early spring, remove dead or crossing branches to maintain shape and encourage blooms (flowers form on old wood).
- Hard Pruning: Late winter, cut back to 6-8 inches above ground for rejuvenation; promotes lush foliage but reduces blooms.
- Tree Form: Prune to a single leader, removing lower branches over time.
- Wear gloves to avoid sap irritation; disinfect tools to prevent disease spread.
Fertilization
- Minimal needs; avoid high-nitrogen fertilizers to prevent excessive growth at the expense of color.
- Apply a balanced, slow-release fertilizer (e.g., 10-10-10) in early spring if soil is very poor.
Pests and Diseases
- Generally pest-resistant; occasional issues include leaf spot, rust, or verticillium wilt.
- Monitor for scale or spider mites in hot, dry conditions; treat with horticultural oil if needed.
- Susceptible to root rot in poorly drained soils; ensure proper drainage.
Propagation
- Cuttings: Take 4-6 inch semi-hardwood or softwood cuttings in late spring; dip in rooting hormone, plant in well-draining mix, keep moist.
- Seeds: Slow and unreliable due to high infertility; rarely used for ornamental cultivars.
Maintenance Tips
- Tolerates drought and poor soils once established, making it low-maintenance.
- Remove suckers at the base to maintain a tidy appearance or single-trunk form.
- Monitor for sap-related dermatitis; wash skin immediately if exposed.
Challenges
- Avoid planting in frost pockets or overly wet soils to prevent winter damage or root issues.
- Purple cultivars may fade to green in shade; ensure adequate sunlight.