*Callistemon*, bottlebrush: plant, prune, maintain

Botany

The genus Callistemon comprises around thirty species of trees and evergreen bushes that thrive in moist soils near waterways in the temperate regions of Australia. The Callistemon, commonly known as “Bottlebrush” or “brush plant”, belongs to the Myrtaceae family, like its relatives eucalyptus, myrtle, and Leptospermum. It is sometimes confused with Melaleuca, with which it shares a striking resemblance.

Callistemon citrinus, Callistemon rigidus, and the highly floriferous Callistemon viminalis and Callistemon laevis are the most common in gardens that experience mild winters. They have given rise to many cultivars that are more cold-resistant. Its growth is relatively fast if not pruned by the cold. It can live for many years.

It flourishes into a beautiful bush, with a lovely bushy habit in its youth, sometimes not exceeding 1 m in height but can also become a small tree reaching up to 10 m with stems that are sometimes slightly arched or very trailing.

The habit varies depending on the species and varieties; rounded, semi-weeping over time, somewhat stiff in Callistemon rigidus, it softens into a fountain shape in Callistemon viminalis, also known as weeping Callistemon. It has a beautiful bark that is reddish-brown or grey-brown in fissured strips and decorative in some species.

The evergreen, leathery foliage is elegant all year round. It consists of long, narrow leaves measuring 2 to 15 cm, alternate, elongated, and pointed, sometimes so tapered that they resemble needles. It is quite sparse in Callistemon rigidus. Juvenile leaves have a silky appearance, pubescent and emerge in spring as young shoots tinged with purple, orange-grey, or salmon-red at bud burst, which later become glabrous, light green, bright green, acid green, grey-green to dark green. In Callistemon citrinus, the aromatic leaves release a scent of eucalyptus and lemon when crushed.

Callistemon is valued for its summer flowering that is as original as it is dazzling, in the form of colourful brushes that have earned it the vernacular name “bottlebrush.” From May-June, for a month, then more sporadically in autumn, small flowers with 5 very short petals gathered in cylindrical spikes appear on a slender stem at the tips of young shoots.

They bear very long stamens beautifully dusted with golden yellow pollen, resembling brushes. They are topped with a tuft of young shoots. The colour of the flowers and the habit vary according to the species.

The development of a Callistemon flower

Embracing the entire shrub, these upright or slightly drooping inflorescences can measure up to 15 cm long and give the plant a pendulous or, conversely, shaggy appearance.

These feathery floral spikes, most often a bright red sometimes almost fluorescent, also display softer shades, ranging from pure white to cream (Callistemon citrinus ‘White Anzac’), to mauve (Callistemon ‘Violaceus’) or even lemon yellow (Callistemon pityoides). The flowers of Callistemon citrinus exude a delightfully lemony fragrance.

Flowering occurs in successive waves and can renew up to 4 times a year, from June to August-September depending on the climate: the terminal bud repeatedly develops new leaves, then new brushes, particularly at the end of summer.

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

Callistemon is highly appreciated by bees.

The deflowered spikes produce small fruits measuring 4 to 6 mm in the shape of spherical capsules, partially embedded in the bark of the branch. These small, very hard shells contain fine brown seeds like dust. Callistemon is a pyrophilous species; the passage of fire causes the fruits to burst open and promotes the germination of dormant seeds.

Callistemon is a rather frost-sensitive plant, hardy down to about -5°C/-8°C, sometimes down to -12°C in well-drained soil, for the least frost-sensitive varieties. However, it is easy to grow in regions with mild winters. In open ground, it should therefore be reserved for Mediterranean or Atlantic climates where it can be used as a specimen or in a free hedge. In cold climates, it will be planted in a pot and kept as a conservatory plant.

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

Species and main varieties

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Callistemon citrinus Splendens - Bottlebrush

A relatively hardy compact cultivar (-7°/-8°C) perfect for pot cultivation. In the garden, it will be more floriferous in soil that is not too dry, without excess lime.

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

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Callistemon rigidus - Bottlebrush

It is the hardiest, most tolerant of soil, and most drought-resistant of the red-flowered Callistemons!

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

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Callistemon viminalis - Bottlebrush

It has a beautiful weeping habit, fine and elegant evergreen foliage, and a dazzling spring flowering! It can be planted in a line to form a screen, or even as a specimen in a small garden.

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

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Callistemon viminalis Hot Pink - Bottlebrush

We love the unique colour of the bright pom-pom inflorescences and the silhouette of this large weeping bush!

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

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Callistemon laevis - Bottlebrush

A less hardy variety (-5°/-7°C), drought-resistant. It will be more floriferous in soil that is not too dry, without excess lime.

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

See the product sheet

Young plantation

Where to plant a bottlebrush

The Callistemon is cultivated differently from one region to another. Generally, rather not very hardy, it withstands frosts of around -8°C but the aerial parts can be damaged by the cold from -5°C. The hardiest, such as Callistemon citrinus, can withstand temperatures of around -10 to -12°C for short periods.

Its cultivation in open ground should be reserved for regions where winters remain mild and where frost does not last too long. You can plant it without any problem in open ground south of the Loire. Resistant to wind and sea spray, it is also a good plant for coastal areas, ideal for seaside gardens.

In regions where frosts are frequent but brief and not intense, place it in a south-facing position sheltered against a wall.

In open ground, it thrives in the sun, protected from prevailing winds to preserve its rather brittle stems, especially when they bend under the weight of the flowers. It also accepts partial shade, where it will be less floriferous.

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

While it can grow in poor, relatively dry soil, the Callistemon will prefer cool soils in summer and greatly appreciates watering in dry climates.

Plan for a location that suits its size: growing rapidly, it will quickly form an imposing bush, sometimes exceeding 6 m in height and nearly 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 the 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 the substrate to dry out between waterings.

In pot as well as in open ground, the Callistemon brings a beautiful originality to gardens and terraces. It can be placed in the centre or background of a flowerbed, either as a specimen plant or in a free or evergreen hedge.

When to plant Callistemon

The planting of callistemon is preferably done in April-May when 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 achieve. If your soil tends to be calcareous, add a mixture of heather soil and potting soil to your garden soil. The callistemon prefers to have the roots well cool in summer and should never show signs of dehydration: waterings must therefore be abundant and regular throughout the hot season, if the leaves of the callistemon dry out, it will not recover.

In open ground

• Dig a hole 3 to 5 times wider than the root ball
• Make a good bed of gravel at the bottom of the hole
• Plant the bush at collar level in the centre of the hole in a mixture of compost, potting soil, ground horn powder, coarse sand, and garden soil
• Fill the hole while keeping the bush upright
• Firm down with your foot
• Mulch around the base of the plant
• Water generously at planting and then once or twice a week throughout the hot season, especially during the first summers
• Space out waterings in autumn and stop them in winter

In pot

Good drainage is essential. It will also have increased water needs but be careful of excesses that would cause its foliage to yellow!

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

As soon as the risk of frost has passed, take the Callistemon out into the garden to enjoy the warm season.

Maintenance and care

Callistemon is easy to grow in mediterranean regions or along the Atlantic coast with mild winters.

Once well established, it requires little attention and will become increasingly drought-resistant. Potted Bottlebrushes require more maintenance than Callistemons planted in the ground.

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

It prefers to have its roots cool in summer and warm during the cold season. Mulch the base of the bush in autumn to protect it from frost, especially during the first winters. In case of severe frosts forecasted, protect the aerial parts with a winter cover and, in cold climates, follow our advice: Callistemon, Bottlebrush: how to protect it from the cold in winter?

In pots

Water regularly throughout the summer. During growth, to encourage flowering, apply a good slow-release fertiliser once or twice a year. Bring it into a cold greenhouse during winter where the temperature will not drop below 7 °C. Continue to water it about once a month. Renew the substrate after 4-5 years, doing so after flowering.

When and how to prune a Bottlebrush?

Callistemon must be pruned just after flowering to maintain a bushy habit. Pruning stimulates flowering, encourages the regrowth of branches, and helps to keep a nice compact habit. Pruning also helps to prevent fruiting that could exhaust the plant.

• Intervene at the end of flowering or in late autumn to correct the habit
• Maintenance simply involves removing weak shoots, dead wood, and branches broken by the wind at the end of winter
• To encourage floral resurgence: remove faded inflorescences as they appear
• If you wish to reduce its growth to maintain a compact habit, it can occasionally tolerate severe cutting back

Diseases and potential pests

Callistemon is not very sensitive to pests and resists diseases well; however, plants grown in greenhouses may be more susceptible to parasites.

In case of an invasion of red spider mites, apply sprays of 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.

The larvae of sawflies or false caterpillars can literally devour the leaves like voracious lace-makers! A solution of black soap may be sufficient to get rid of them.

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

In overly calcareous soil, or in case of excess water, the leaves turn yellow due to chlorosis. Good drainage and regular applications of compost and heather soil by scratching at the base of the bush can sometimes prevent its occurrence.

→ Learn more about diseases and pests of Callistemon in our advice sheet.

Multiplication

The multiplication of callistemon by sowing seeds is possible (provided you heat the seed capsules over a candle flame beforehand!) but flowering will only occur 3 to 6 years later. Semi-hardwood cuttings taken at the end of summer are simpler and more reliable to carry out. Rooting can take a long time, but flowering occurs in the first year.

• At the end of summer, take semi-ripe shoots of 10 to 15 cm just below an eye (that is, in the phase of transformation from soft wood to hard wood)
• Make a longitudinal cut in the bark for 5 cm
• Remove the leaves from the lower third
• Plant them in a light and well-draining mix of sand and potting soil
• Keep the substrate moist until rooting, which can take several months
• Pot your cuttings in the following spring or plant them out permanently
• Water well in the first year after planting

→ Learn more in our tutorial: Propagating a Callistemon

Associate

Particularly remarkable for the luminous or incandescent explosion it offers throughout the summer, the callistemon or “Bottlebrush” thrives in all natural and wild gardens. Along 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 perennial border, or grouped in free hedges. It creates lush and generous summer scenes.

It will be sensational in a evergreen hedge, alongside a bushy ceanothus (‘Skylark’), a summer-flowering broom (Cytisus scoparius ‘Apricot Gem’), accompanied by myrtles or oleanders.

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

In a free hedge, it easily associates with a Caesalpinia gillesii and Buddleias. With its distinctive silhouette, it makes a good partner for tamarisks, hibiscus, and smoke trees.

It tolerates salt spray well, making it a beautiful bush for a mixed hedge in coastal gardens.

As a specimen in the centre of a low or creeping plant border 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 highlight its spectacular flowering.

You can surround its base with summer-flowering perennial shrubs like red-flowered Salvias.

Create a perennial border with accents of garrigue using lavenders, creeping rosemaries, and euphorbias to accompany it.

In a more exotic-style border, it can be paired 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 will pair well with an orange tree or mimosa.

→ Discover more association ideas with Callistemon in our advice sheet!