<em>Callistemon</em>, bottlebrush: planting, pruning, care

Botany

Genus Callistemon includes around thirty species of trees and bushes with evergreen foliage, native to moist soils near waterways in temperate regions of Australia. Callistemon, commonly called “bottlebrush” or “bottle-brush plant”, belongs to family Myrtaceae like its cousin eucalyptus, myrtle and Leptospermum. It is sometimes confused with Melaleuca with which it bears a striking resemblance.

Callistemon citrinus, Callistemon rigidus, and the very floriferous Callistemon viminalis and Callistemon laevis are the commonest in gardens with mild winters. They have given rise to many cultivars more resistant to cold. Growth is fairly rapid if not cut back by frost. Plant can live for many years.

It develops into an attractive bush, with a pleasing dense habit in youth, sometimes remaining shrub-like not exceeding 1 m in height but also able to become a small tree reaching up to 10 m with stems sometimes slightly arching or very trailing.

Habit varies according to species and varieties; rounded, semi-weeping with age, somewhat stiff in Callistemon rigidus, softening into a fountain habit in Callistemon viminalis (also called Callistemon pleureur). It has attractive reddish-brown or grey-brown bark in fissured strips, decorative on some species.

Evergreen foliage, leathery, is elegant all year round. It consists of long narrow leaves 2–15 cm, alternate, elongate and pointed, sometimes so tapered they resemble needles. Foliage is fairly sparse on Callistemon rigidus. Juvenile leaves take on a silky, pubescent appearance and emerge in spring as young shoots tinged purple, grey-orange or salmon-red at bud burst period, later becoming glabrous and ranging from light green, bright green, lime green, grey-green to dark green. In Callistemon citrinus, aromatic leaves give off an aroma of eucalyptus and lemon when crushed.

Callistemon is prized for its summer flowering, as original as it is dazzling, in the form of colourful bottlebrushes that earned it the vernacular name “bottlebrush”. From May–June, for about a month, then more sporadically in autumn, small 5-petalled flowers with very short petals gathered in cylindrical spikes borne on a thin stem at the tip of young shoots appear.

They bear very long stamens prettily dusted with golden-yellow pollen, making them resemble bottlebrushes. They end with a tuft of young shoots. Flower colour and habit vary according to species.

Development of a Callistemon flower

Illuminating the whole bush, these erect or slightly pendulous inflorescences can reach up to 15 cm long and give plant a pendulous or, conversely, bristly aspect.

These plume-like flower spikes, most often a vivid red sometimes almost fluorescent, also show softer shades, from pure white to cream (Callistemon citrinus ‘White Anzac’), to deep pink (Callistemon viminalis ‘Hot Pink’), to mauve (Callistemon ‘Violaceus’) or even lemon-yellow (Callistemon pityoides). Flowers of Callistemon citrinus give off delightfully lemony scents.

Flowering occurs in successive waves and can repeat up to 4 times a year, from June to August–September depending on climate: terminal bud repeatedly produces new leaves and then new bottlebrushes, especially at the end of summer.

Melliferous and nectariferous, the flowers attract many foraging insects and pollinators such as bees and butterflies.

Callistemon is much appreciated by bees.

Spent spikes produce small fruits 4–6 mm in the form of spherical capsules, half embedded in the branch bark. These very hard little shells contain brown seeds as fine as dust. Callistemon is a pyrophilous species; passage of fire causes fruits to burst and favours germination of dormant seeds.

Callistemon is somewhat tender, hardy to about −5°C/−8°C, sometimes down to −12°C in well-drained soil for the least frost-sensitive varieties. It is however easy to grow in regions with mild winters. In open ground, reserve it for Mediterranean or Atlantic climates where it will be used as a specimen or in an informal hedge. In cold climates, plant in a container and keep as an orangery plant.

It thrives in full sun or partial shade in fertile, light, well-drained soil, moist to dry in summer.

Species and main varieties

Most popular

Our favourites

Callistemon citrinus Splendens - Bottlebrush

Relatively hardy cultivar (-7°/-8°C), perfect in a pot. In garden, more floriferous in soil not too dry and without excess lime.

• Flowering time July to September
• Height at maturity 2,50 m

See the product sheet

Callistemon rigidus - Bottlebrush

Hardiest, most tolerant regarding soil and most drought-resistant of red-flowering Callistemon!

• Flowering time June, July
• Height at maturity 2,50 m

See the product sheet

Callistemon viminalis - Bottlebrush

Has a beautiful weeping habit, fine elegant evergreen foliage and a dazzling spring flowering! Plant in a row to form a screen, or as a specimen in a small garden.

• Flowering time June to October
• Height at maturity 7 m

See the product sheet

Callistemon viminalis Hot Pink - Bottlebrush

We love the unique colour of the bottlebrush inflorescences, so luminous, and the silhouette of this large weeping bush!

• Flowering time June to October
• Height at maturity 1,70 m

See the product sheet

Callistemon laevis - Bottlebrush

Low-hardy variety (-5°/-7°C), drought-resistant. More floriferous in soil not too dry and without excess lime.

• Flowering time June to October
• Height at maturity 1,80 m

See the product sheet

Planting

Where to plant a bottlebrush

Callistemon is grown differently from one region to another. Generally not very hardy, it withstands frosts down to around −8°C but aerial parts can be damaged by cold from about −5°C. Hardier forms such as Callistemon citrinus can resist temperatures of around −10 to −12°C for short periods.

Cultivation in ground should be reserved for regions where winters remain mild and where frost is not prolonged. You can plant it outdoors without problem south of Loire. Wind- and salt-spray-resistant, it is also a good plant for seaside planting, ideal for coastal gardens.

In regions where frosts are frequent but brief and light, place it in a south-facing position sheltered against a wall.

In ground, it thrives in sun, protected from prevailing winds to preserve its fairly brittle stems, especially when they arch under weight of flowers. It also tolerates partial shade where it will, however, be less floriferous.

It adapts to almost all soils, fresh or dry in summer. It grows in non-calcareous soil, fairly fertile. In deep soil, once well established, it will show increased drought resistance. A slightly stony or sandy soil, slightly acidic to neutral, provided it is well drained, will suit it just as well. Some species (Callistemon pallidus), native to marshy edges of Australian coast, tolerate temporary flooding and poor drainage.

If able to grow in poor, relatively dry soil, Callistemon will prefer soils that stay cool in summer and greatly appreciates watering in dry climates.

Allow ample space: fast-growing, it will quickly form a large bush sometimes exceeding 6 m in height and almost as wide. Some species such as the weeping Callistemon can reach 8 to 10 metres in height in our latitudes.

In harsher climates, in regions north of Loire, prefer planting in a large container to be stored for winter in an unheated greenhouse or conservatory. Ensure good drainage and water abundantly, allowing substrate to dry between waterings.

In a pot as well as in ground, Callistemon brings striking originality to gardens and terraces. It can be placed centre or at back of a border, as an isolated specimen as well as in loose or evergreen hedging.

When to plant Callistemon

Planting of callistemon is best done in April–May once all risk of frost has passed, or in early autumn in very mild climates.

How to plant a Callistemon

Planting a Callistemon is easy to succeed. If soil tends to be calcareous, add a mix of heather soil and leaf mould to garden soil. Callistemon likes roots kept cool in summer and must never show signs of dehydration: waterings must therefore be abundant and regular throughout warm season; if Callistemon leaves dry out, it will not recover.

In ground

• Dig a hole 3 to 5 times wider than rootball
• Make a good bed of gravel at base of planting pit
• Plant bush with collar level at centre of hole in a mix of compost, potting compost, ground horn meal, coarse sand and garden soil
• Backfill while keeping bush upright
• Firm down with foot
• Mulch base of plant
• Water copiously at planting then once to twice a week throughout warm season, especially during first summers
• Reduce watering in autumn and stop in winter

In a pot

Good drainage is essential. It will also have increased water needs but beware of excesses that would yellow foliage!

• In base of a pot at least 50 cm in diameter, spread a good drainage layer (gravel or clay balls)
• Plant in a slightly sandy substrate enriched with leaf mould and mulch the base
• In summer, water generously as soon as soil is dry, about twice a week
• In winter, water very sparingly
• Apply a slow-release fertiliser in spring
• Bring pot into frost-free shelter at first cold snaps in cold regions

As soon as risk of frost has passed, move Callistemon outdoors so it can enjoy warm season.

Care and maintenance

Callistemon is easy to grow inMediterranean regions or on the Atlantic coast with mild winters.

Once established, it requires little attention and will become increasingly drought‑tolerant. Potted bottlebrushes require more maintenance than in‑ground callistemons.

Callistemon likes cool soil in summer. Throughout the warm season, water thoroughly and regularly once or twice a week, to keep the base cool but above all not waterlogged. Space out watering frequency in autumn and stop them in winter.

It likes roots to be cool in summer and warm during the cold season. Mulch base of bush in autumn to protect it from frost, especially during first winters. If severe frosts are forecast, protect aerial parts with a fleece and, in cold climates, follow our advice: Callistemon, Bottlebrush: how to protect it from the cold in winter?

In a pot

Water regularly throughout summer. During growth, to encourage flowering, apply a good slow‑release fertiliser once or twice a year. Bring it into a cool glasshouse for winter where temperature will not fall below 7 °C. Continue to water it about once a month. Renew potting compost after 4–5 years; do this after flowering.

When and how to prune bottlebrush?

Callistemon must be pruned immediately after flowering to keep a bushy habit. Pruning helps stimulate flowering, branch regrowth and also maintain an attractive compact habit. Pruning also prevents fruiting that could exhaust the plant.

• Carry out pruning at end of flowering or late autumn to correct habit
• Maintenance simply involves removing in late winter weak shoots, dead wood and branches broken by wind
• To encourage repeat flowering: remove spent inflorescences as they appear
• If you wish to reduce its growth to maintain a compact habit, it will tolerate occasional severe pruning

Diseases and potential pests

Callistemon is not very susceptible to pests and resists diseases well, however plants grown in greenhouses can be more vulnerable to parasitic pests.

If infested with red spider mites, spray with soapy water.

It can also be attacked by scale insects. Treat with sprays of rapeseed oil. Repeat two or three times at 15-day intervals.

Sawfly larvae or false caterpillars can literally gobble up leaves, turning them into lace! A black soap solution may be enough to deal with them.

The Cylindrocladium scoparium, a fungus naturally present in Myrtaceae, can cause spots on the foliage and stem necroses.

In overly calcareous soil, or when waterlogged, leaves yellow through chlorosis. Good drainage and regular additions of compost and heather soil, worked in by light hoeing around the base of the bush, can sometimes prevent this.

→ Learn more about diseases and parasitic pests of Callistemon in our care sheet

Propagation

Propagation of callistemon by sowing seeds is possible (provided seed capsules are heated over a candle flame first!) but flowering occurs only 3 to 6 years later. Semi-ripe cuttings taken at end of summer are easier and more reliable. Root formation can be slow but flowering occurs from first year.

• At end of summer, take semi-ripe shoots 10 to 15 cm long, cutting just below an eye (i.e. in transition from soft wood to hard wood)
• Make a 5 cm lengthwise cut in bark
• Remove leaves from lower third
• Plant them in a light, free-draining mix of sand and potting compost
• Keep growing medium moist until roots form, which can take several months
• Pot up cuttings following spring or plant out permanently
• Water well during first year after planting

→ Learn more in our tutorial : Propagate a Callistemon

Associate

Callistemon, or “Bottlebrush”, is particularly remarkable for the luminous, almost incandescent display it offers throughout summer; it thrives in all natural and wild gardens. On the Mediterranean coast or in an Atlantic climate, it can be planted almost anywhere in the garden, as a specimen, at the back of a border of perennials, or grouped into informal hedges. It creates abundant, generous summer scenes.

It will be sensational in an evergreen hedge, with a shrubby ceanothus (‘Skylark’), a summer-flowering broom (Cytisus scoparius ‘Apricot Gem’), together with myrtles or oleanders.

An example of an association in an evergreen hedge: Nerium oleander – Ceanothus ‘Skylark’ – Myrtus communis – Callistemon viminalis

In an informal hedge, it pairs easily with Caesalpinia gillesii and with Buddleias. With its distinctive silhouette, it is a good partner for tamarisks, hibiscus and smoke trees.

It tolerates sea spray well, which makes it a very fine bush for mixed hedges in seaside gardens.

As a specimen at the centre of a bed of low or groundcovering plants or in a large rockery, it will be magnificent surrounded by sun-loving perennials such as small cistus, Linaria purpurea, Oriental poppies, echinaceas, coreopsis and rudbeckias that will set off its spectacular flowering.

Its base can be surrounded by shrubby perennials that flower in summer, such as red-flowered Salvias.

Create an evergreen border with garrigue accents by accompanying it with lavenders, creeping rosemary and euphorbias.

In a more exotic-style border, pair it with its Australian cousins such as Phormium, Melaleuca gibbosa, Grevillea rosmarinifolia and Leptospermum.

An example of an exotic association: Callistemon viminalis – Grevillea rosmarinifolia – Phormium – Melaleuca gibbosa and Leptospermum scoparium ‘Red Damask’.

In a greenhouse or conservatory, it pairs well with an orange tree or a mimosa.

→ Discover other ideas for pairing with Callistemon in our advice sheet!