Callistemon is a genus of evergreen trees and shrubs from Australia that get their common name "bottlebrush" from their striking flowers characterised by large, showy stamens. Indeed, the genus takes its name from the Greek for "most beautiful stamen". They have been grown in Europe since a specimen of C. citrinus was introduced to Kew Gardens by botanist Joseph Banks in 1789.
Unsurprisingly, Callistemon like to grow in full sun and warm climates in moderately moist, neutral or acid soils. Different varieties produce either red, white or yellow flowers in showy spikes that can be as long as 15cm. C. citrinus is a particularly common variety for landscapers due to the vibrant red flowers that are borne on arching branches in profusion during spring and summer. An ideal position would be against a sunny wall where the plant would be sheltered from cold winds during the winter, or in a shrub border.
Callistemon plants are relatively slow-growing. Species such as C. salignus Award of Garden Merit (AGM) can reach up to 15m in height while others, such as C. citrinus 'White Anzac', are ground-hugging plants that grow no taller than 1m. The leaves are linear to lanceolate and are not shed in winter. The spiked ends can scratch the skin, making them a candidate for "security planting".
Bushes can become straggly it not pruned when young. Most established plants do not need routine pruning, but those that have outgrown their position in a planting scheme can be reduced in size by cutting back older wood in stages over the summer. This also encourages the growth of new shoots from the base.
The bottlebrush shrub usually flowers from early spring through to early summer, depending on where they are grown. Each flower head produces a profusion of seed capsules that remain close to the stem until they are stimulated to open, either by the heat from a bush fire or when the plant dies. A few species of bottlebrush do release their seeds annually and plants can be propagated by collecting the seeds or by taking cuttings.
Callistemon is attacked by few pests, although red spider mites and scale insects may become a problem. In general, the genus will tolerate quite cold winters, although prolonged periods of cold and wet can damage and even kill some species.
WHAT THE SPECIALISTS SAY
Paul Culora, salesman, Classiflora, Hertfordshire: "The best one is C. laevis (also known as C. rugulosus). It has been a good seller for us and we have been doing it for quite a few years, but this year has been a bit slower. I don't know if it's the weather or just people not buying as many.
"We mostly sell to garden centres but landscapers want it more and more. Toughness is a question mark - a lot were lost last winter because of the bad weather, but prior to that they grew well for many years. In garden centres they are an impulse buy because of the colour."
Angela Tandy, director, The Old Walled Garden Nursery, Warwickshire: "We hold the National Collection of more than 60 here, though some are hardier than others - a few succumbed this winter.
"People enjoy being able to get different varieties. The yellow C. pallidus 'Candle Glow' and red and white C. pallidus 'Father Christmas' are well worth a try. They need well-drained and nourished soil and should be kept trimmed after flowering because they look better when deadheaded.
"There are no real pest and disease problems with no greenfly. C. citrinus 'Splendens' AGM is well-tried, as is the purple-flowered C. paludosus. When people do see the different varieties such as purples in flower looking like they have gold brushed on the edges of the petals, they think they are lovely. We grow ours from cuttings from registered hybrids and cultivars."
Simon Lowndes, partner, MacPenny's Nurseries, Dorset: "When they are in flower they sell themselves. The rest of the year is not so easy. The issue is getting them through the winter - a lot of varieties don't like the cold too much. It's about choosing the right varieties.
"The toughest is C. linearis AGM but it's not the most spectacular. The most floriferous and best seller is C. citrinus 'Splendens' AGM, but they have got caught in the last two winters, although they haven't died. We do six or seven varieties and the others sell on a par below 'Splendens' because 'Splendens' flowers more freely. We sell a few to landscapers but our main customer is the public.
"To look after them, make sure you choose the right spot - free-draining and hot and sunny, preferably up against a south-facing wall or fence in lime-free soil. As young plants, make sure they are sheltered and protected from fleece in winter."
Mike Hodges, garden designer, Hambrooks, Hampshire: "I use bottlebrush a fair bit. People love their big over-the-top flowers - everyone who sees them says 'wow'. There is a lovely dwarfish creamy one, C. sieberi. They also have interesting foliage and are evergreen too, which is useful.
"We do all private work within 35 miles of Southampton and the weather our way suits them - we don't have a problem with cold hitting them in the winter."
SPECIES AND CULTIVARS
C. citrinus produces an abundance of crimson-red flowers in spikes between 5cm and 15cm long during the summer on long willowy branches. Variable in size, its height and spread range from 1.5m to 8m.
C. citrinus 'Firebrand' is a low-spreading variety producing silvery pink young shoots and crimson flowers. It grows to a height of 1.5m and spread of 4m.
C. citrinus 'Splendens' AGM (H3) has broad leaves and pinkish-red young shoots.
C. citrinus 'White Anzac' bears white flowers that become tinged with pink when mature. This variety does not grow as wide as others, making it better for small spaces.
C. 'Kings Park Special' has red flowers that are borne on spikes up to 10cm long. It grows to a height and spread of 2m to 4m.
C. laevis syn C. rugulosus is the scarlet bottlebrush due to its vibrant red flowers that appear in mid spring and last until mid summer. The stamens are rosy red but the anthers are yellow, giving the flowers a speckled appearance. A large shrub, growing to 4m to 5m, width 2.5m to 3m.
C. linearis AGM (H3) has narrow, rigid, dark-green leaves with points on them. It bears red flowers in spikes up to 10cm in length from late spring to autumn.
C. macropunctatus has red flowers born in spikes from early summer to autumn. It grows to a height and spread of 2m to 4m.
C. 'Mauve Mist' has mauve pink flowers that fade with age in spikes up to 10cm long in the summer. The leaves are tapered at each end and mid green. Height and spread 2m to 4m.
C. pallidus has creamy yellow flowers that appear in the spring and last until mid summer. Height and spread 2m to 4m.
C. pallidus 'Candle Glow' produces vibrant yellow flowers.
C. pallidus 'Father Christmas' has bicoloured flowers with stamens that are off-white grading to pink at the base.
C. pinifolius is known as the pine bottlebrush with rigid, linear, sharply-pointed dark-green leaves that can be 10cm in length. It bears yellow flowers in spikes up to 8cm long in summer. It grows to a height of 1.5m and spread of 2.5m.
C. pityoides is a compact variety also known as the alpine bottlebrush. It grows to a height of 1.5m and spread of 1m, producing yellow flowers in smaller spikes of 4cm in length in mid to late summer.
C. salignus AGM (H3) is also known as the willow bottlebrush. This species can grow up 15m tall, with a spread of 5m. It has delicate lemon-coloured flowers and papery white bark.
C. sieberi syn C. paludosus is a smaller variety of bottlebrush with a height and spread of 1m to 2m. It has creamy yellow flowers in spikes of up to 15cm from late spring to summer. It grows to a height and spread of 1m to 2m.
C. viminalis is known as the weeping bottlebrush due to its weeping stems with lance-shaped dark-green leaves. A large upright bush, it can grow to 10m by 4m. It bears bright red flowers in spikes 10-20cm long from spring to late summer.
C. viminalis 'Captain Cook' is a dense, compact variety with a height and spread of 1.5m to 2m. It features bright red flowers and mid-green leaves.
C. viminalis 'Rose Opal' is compact and has red flowers that fade to pink as they age.
C. viridiflorous bears yellow-green flowers and has densely arranged sharp-pointed dark-green leaves. It grows to a height of 1.5m and spread of 2m.