Smoke bush: pruning, propagation & varieties

Smoke bushes show off their colourful foliage and hazy plumes of flowers in summer as well as the colder months.

Both the foliage and seed heads of the smoke bush (Cotinus coggygria) contribute to its ornamental value. Its wispy smoke-like appearance draws the attention of every passerby. Read on to find out how to prune and propagate a smoke bush and discover a few of the most popular varieties.

Smoke bush: characteristics and origin

The smoke bush, also called smoke tree, cotinus plant or dyer’s sumach, belongs to the sumac family (Anacardiaceae), which includes sumac (Rhus). Smoke bushes are native to numerous regions including the Mediterranean, southern Europe, south-western Asia, north-western India, China, Pakistan and Nepal. They have even become naturalised in some parts of the UK. Their natural habitats are characterised by coarse, poor to moderately fertile, calcareous soils. These large shrubs are found on dry, warm slopes, reaching from lowlands up into mountainous regions.

Smoke bushes are deciduous and have an upright, wide and bushy or open growth habit. They can reach heights and widths of 3 to 5m. There is also a dwarf variety which is suitable for growing in a pot. Smoke bushes are only hardy down to about -20° C, so keep this in mind if you are considering planting one. The bark of a smoke tree is tinged grey and slightly cracked. The ovate, smooth leaves have entire margins and are alternate.

The foliage of a cotinus smoke bush is originally green, but it can also be red or yellow depending on the variety. In autumn, the leaves turn orange to scarlet. The inconspicuous and yellow smoke bush flowers have five petals and are arranged loosely in large, hairy panicles. They usually appear from June to July and eventually develop into the namesake’s wispy seed pods. These seed pods often remain intact and have ornamental value into December.

The most beautiful smoke bush varieties

There are several varieties of smoke bush, which differ mainly in their growth, size and colour. Here are some of the most beautiful Cotinus coggygria varieties:

• Cotinus coggygria ˈRoyal Purpleˈ: this popular slow-growing variety reaches a height and width of up to 3m, has dark red foliage and yellow or cream-coloured flower panicles.

• Cotinus coggygria ˈGolden Spiritˈ: this variety paints a different picture with its golden-yellow foliage and red-tinted flowers. It grows 2 – 2.5m tall and 1.5 – 2m wide. The fruit clusters of this variety are dark red.

• Cotinus coggygria ˈLillaˈ: this low-growing and compact version of ˈRoyal Purpleˈ is limited to a height and width of about 1.5m, making it suitable for planting in containers or small gardens. The leaves are dark purple and the flowerheads are yellow or red.

• Cotinus coggygria ˈSmokey Joeˈ: this medium-size cultivar bears green foliage and pink fruit clusters with a height and width of up to 2.5m.
  
• Cotinus coggygria ˈYoung Ladyˈ: the flowers of this low-growing, green-leaved variety are yellow and pink in colour, while the fruit is light brown. It can also reach a height and width of 2.5m.

Planting a smoke bush

The ideal place to plant a smoke bush depends on the colour of its leaves. For a red smoke bush to display its colours to their full intensity, choose a warm and sunny location. Smoke tree varieties with green or yellow leaves prefer partial shade. No matter the leaf colour, a smoke bush needs a sheltered spot in regions with harsh winters. As for soil conditions, these plants aren’t particularly demanding. Well-drained, dry to moist soil that is slightly acidic to highly calcareous is ideal. Smoke bushes grow best in poor soil but also tolerate moderately fertile substrate.

Tip: to prevent verticillium wilt, loosen compacted and heavy soil by mixing in some stones or quartz sand.

To improve the soil and increase its permeability, add some lime to your smoke tree’s soil. To find the appropriate dosage of lime and apply it properly, it is important to first find out the soil pH and identify the soil type.

The best time to plant a smoke bush is from September to October, but you can also do so as early as mid-May. Once you have found a suitable location, dig a planting hole twice the size of the smoke bush’s root ball. Enrich especially sandy substrate with high-quality planting soil or a little compost. Our peat-free Plantura Organic Enriched Compost is suitable for this as it increases the soil’s fertility over a long period of time and also stimulates soil activity. Place your smoke bush in the planting hole at ground level. After filling in any gaps with soil, gently compact the substrate and water thoroughly.

Red smoke bushes are typically planted as solitary shrubs, making for impressive focal points. On the other hand, the ˈGolden Spiritˈ is often kept as a small hedge or privacy screen. When growing smoke bushes as a hedge, keep a 1m planting distance between plants. If you are planning on planting other shrubs near the smoke bushes, increase the planting distance to at least 2m.

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If you plan to grow a Cotinus coggygria ˈLillaˈ in a pot, choose a container with a capacity of at least 30 litres. Later, when the shrub has grown larger, move it to a 50-litre container. Ensure the container has drainage holes and place a drainage layer of expanded clay at the bottom. Then, fill the pot with a mixture of high-quality planting soil and about a third sand to improve permeability.

What to plant with smoke bushes: if you want to showcase your smoke tree alongside other plants, try planting vitex (Vitex agnus-castus) and ornamental grasses such as Chinese silver grass (Miscanthus sinensis). Both go well with a showy smoke bush that grabs all the attention and they develop attractive flowers and seed pods at different times to complement the smoke tree’s wispy seed pods. Try combining green- and yellow-leaved smoke bushes with red-barked dogwoods (Cornus alba) or common dogwoods (Cornus sanguinea) for an equally interesting aesthetic. The round and colourful leaves of barberry species also pair well with smoke bushes.

Cotinus care

Caring for a smoke bush is far from arduous. Once the ornamental shrub is established in your garden, it is not only reliably hardy but also heat and drought tolerant. Smoke bush plants do not require many nutrients and rarely require pruning.

Smoke bush pruning

Smoke bushes will thrive and flower even without proper care, so regular pruning is not a must. However, to prevent them from spreading, remove any shoots growing along the ground at their base. It is also a good idea to remove branches that grow toward the centre of the bush or cross over other branches. Smoke bushes can handle vigorous pruning. They can even be cut back to the trunk every few years, but bear in mind that doing so may mean they won’t bloom the following year.

When to prune a smoke bush: due to their pruning tolerance, you can prune smoke trees at almost any time of year. Just avoid pruning during dry and hot periods as well as during frosts.

Fertilising and watering

If your smoke bush is planted out in the garden, give it a single application of compost in the spring to meet its nutrient needs for the year. As for those kept in containers, apply a liquid fertiliser for flowering shrubs about every 4 weeks.

Tip: applying a layer of autumn leaves or grass clippings as mulch will help the soil retain moisture for longer and also provides some additional nutrients to your plants.

It is important to water newly planted smoke trees regularly, especially during their first year. The consistent moisture supports their growth. But avoid waterlogging, as it can harm the roots and increases the risk of a verticillium wilt infestation, which can be fatal for the shrub. Once the shrub is well established in the garden bed — after about a year — it can cope on its own. Potted smoke bushes need regular watering to prevent the root ball from drying out.

Smoke bushes in winter

Mature smoke bushes are hardy down to -20 °C, a temperature we rarely see here in the UK. However, in particularly harsh environments, additional protection is recommended. Winter protection is also necessary in the first 1 to 2 years after planting, as well as for potted smoke bushes. To prepare a smoke bush for winter, cover its trunk with leaves or brushwood and wrap the container with a fleece or jute to prevent the root ball from freezing. Move your potted smoke tree to frost-free, yet cool winter quarters. While overwintering your smoke tree, water it on occasion — do not allow the root ball to dry out entirely.

Cotinus propagation

Whilst propagating smoke bushes by seed is possible, you’re better off propagating by cuttings or shoots.

When propagating with smoke bush cuttings, do not use the youngest or oldest branches. The branches that can be bent slightly before breaking are ideal. Take cuttings in summer, from July to August, preferably in the morning. To do this, locate sections 8 to 12cm long and cut them just below a leaf node. Keep the cuttings cool and moist until it is time to plant them. To help the cuttings take root, remove the lower leaves and some of the bark, and dip the wounded part in rooting hormone. Then plant the cotinus cuttings in prepared pots with a permeable, moist substrate. To maintain moisture, place a plastic covering over the pot. After a few weeks, enough roots will have formed to move the plants to a larger pot.

Tip: smoke bush cuttings lose moisture through their leaves. To reduce a cutting’s transpiration rate, remove half of the leaves.

Smoke trees sometimes self-propagate when their shoots that grow along the ground form roots. After a while, these will develop into new plants. You can mimic this method of propagation by layering. In spring, locate shoots that are at least 1 year old, and secure them in the ground using a hook. Allow the ends of the shoots to protrude about 30cm from the ground, and scratch the section that is pinned to the ground to promote root development. Remember to keep the soil moist. Once the shoot has enough roots — typically by autumn — separate it from the mother plant and move it to its new location.

Smoke tree uses

As indicated by the name “dyer’s sumach”, the leaves and wood of the smoke bush can be used for dyeing wool and silk fabrics. Harvested parts of the plant can be used straight away or dried for storage. Smoke tree leaves are also used in traditional Russian medicine to treat burns and poisonings. In fact, the fisetin in smoke bushes has been found to be beneficial to humans, for instance by improving memory.

Are smoke trees poisonous?

Smoke bushes are not poisonous, but, being ornamental shrubs, nor are they suitable for consumption. However, smoke bushes do belong to the same family as Atlantic poison oak (Toxicodendron pubescens), which can cause severe dermatitis. As such, smoke bushes may also cause dermatitis for people with sensitive skin. If your skin is very sensitive, wear gloves when pruning this shrub.

Another richly-coloured ornamental shrub is the Chinese fringe flower (Loropetalum chinense), which has wonderful showy flowers.