It's early June at Cincinnati's Spring Grove Cemetery and Arboretum and this purple smoke tree is just beginning to smoke (come into bloom)!
Smoketree is a rounded, broadly spreading, and sometimes multistemmed shrub that grows to 15 ft (4.6 m). The upright branches become open and loose as the plant ages. The purplish brown stems have a waxy bloom when young and develop thin blocky light gray bark as they grow older. The smooth bluish green oval leaves are 1.5-3.5 in (3.8-8.9 cm) long. They are borne alternately on long stems and have parallel veins and rounded or notched tips. In the fall, they turn bright shades of yellow, orange, purple, and red. The actual flowers are inconspicuous little yellowish green blossoms that appear in early summer, but the long pinkish filaments on the stems of the bloom clusters create a striking cloudlike effect through the summer. The fruits are tiny kidney shaped brown berries.
In early October the smoke tree transitions purple leaves to brilliant shades of red and gold.
There are a number of striking purple-leaved cultivars with darker purplish red flowers. 'Royal Purple' is one of the most popular, but least cold hardy. It has leaves that unfurl maroon red, mature to an extremely dark wine purple, then fade to a greenish purple with reddish pink edges before they turn vivid scarlet in the fall. 'Nordine Red' is a very hardy cultivar with dramatic nonfading wine red foliage that turns yellow and orange. 'Notcutt's Variety' has dark maroon foliage and purplish pink plumes. 'Velvet Cloak' has dark velvety rose purple leaves that hold their color well through the summer, then turn intense orange red in the fall. 'Daydream' is a dense green-leaved shrub with exceptionally abundant pink flowers. 'Flame' has green leaves, pink flowers, and good orange red fall color. American smoketree (Cotinus obovatus), which is native to the south-central United States, is a similar species that can grow into a 30 ft (9.1 m) tree. Its pink blossoms are not showy, but it has beautiful gray bark and its foliage turns spectacular shades of orange, purple, gold, and rose red in the fall. 'Grace' is a cross between 'Velvet Cloak' and C. obovatus which can grow into a 25 ft (10.7 m) tree with massive clusters of deep pink flowers. It has large purplish rose leaves that darken to burgundy red, then turn brilliant red orange in the fall.
This is the green leaved variety of smoke tree called 'Daydream'. It decks itself out in puffy pink flowers each year just in time to celebrate the Fourth of July.
Smoketree comes from southern Europe, central China, and the Himalayas, where it grows on dry rocky hillsides and in open woods, usually on limestone.
Smoketree prefers a moderately fertile loam, but it tolerates a broad pH range and adapts well to a variety of soils ranging from light sands to heavy red clays. It will grow on hot, dry, gravelly soils, but is short lived on rich sites. Pruning promotes intense foliage color. Since smoketree flowers on new growth, it can be cut to the ground each winter and grown as a cutback shrub. This treatment yields spectacular growth with heavy flowering and dramatic foliage color on a cluster of 3-5 ft (0.9-1.5 m) shoots. Alternatively, older shrubs can be limbed up to create attractive small trees. Smoketree may be affected by rusts, leafspot, verticillium wilt, or San Jose scale, but it is notably resistant to honey fungus. The purple leaved cultivars are susceptible to mildew. Excessive misting should be avoided.
Light: Sun brings out the best leaf color, but smoketree will tolerate light shade. Moisture: Smoketree prefers well-drained moist to dry soil. It will grow on damp sites, but is prone to root rot in such situations. Deep infrequent watering is ideal. Hardiness: USDA Zones 5 - 8. Most smoketree cultivars will survive close to 0ºF (-17.8ºC). The foliage color of the purple cultivars tends to fade during long hot southern summers. Propagation: Both male and female plants are required for seed production. Sow fresh seeds in a coldframe as soon as they are ripe in the fall. "Green" seeds that are fully developed, but not yet dry and hard, germinate most readily; they can be expected to sprout in the spring. Seeds can be stored for several years. Stored seeds should be warm stratified for 2-3 months at 60ºF (15.5ºC), then cold stratified for 2-3 more months. It may take them a year to germinate at 60ºF (15.5ºC). Smoketree can be propagated from cuttings, but some cultivars are notoriously hard to root. Half ripe heel or nodal cuttings taken in late summer, treated with a rooting compound, and started under mist are probably the best bet. The rooted cuttings should be overwintered in the rooting medium in a coldframe. Trench layering in the spring may also work. Smoketree transplants easily, but may be slow to get established in its new location.
Although the actual flowers are tiny they produce pinkish filaments that combine to create a soft hazy effect (this is 'Daydream').
Smoketree is most often employed for color accent or contrast, but it can also be used as a featured specimen plant or blended with other species in a shrub border. Infusions have been used as a gargle and to stop bleeding, as well as in tanning and dyeing. Both flowers and foliage are excellent for exotic effects in floral arrangements.
Intense color is this plant's most outstanding feature. The purple-leaved varieties can be used to form a dramatic dark backdrop for summer's bright flowers and bright green foliage. Then, as the flowers fade in the fall, the smokebush will take over and light up the landscape with brilliant fall color. The unique billowing cloudlike appearance of the flowering shrub can be used for fantasy effects. All this drama can be possible even if all you have to offer is a dry gravelly soil where it is hard to get anything else to perform well. This species was popular in Victorian gardens and is thus suitable for many garden restoration projects. The flowers attract bees.
Skin contact can cause dermatitis in sensitive people.