Bottlebrushes (Callistemon)
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Bottlebrushes, the shrubs of the genus Callistemon, are among the most widely recognised plants in our gardens and also among the most underrated, abused and misused.
As a child, bottlebrushes were among the first plants I learnt to recognise and I suspect most children are equally fascinated by the unusually shaped flower heads. They're also great for parents as it's hard to mistake a bottlebrush for any other plant, except perhaps a melaleuca or kunzea, so it's easy to appear authoritative when answering the inevitable what's that question.
Regretably, we seem to grow out of that fascination and come to see bottlebrushes as untidy woody-stemmed plants that are fit for nothing but digging out and dumping. I wish I knew why that's so. It seems that many New Zealand gardeners have some sort of hang-up over narrow-leaved plants and those that show a bit of bark. Plants with broad, deep green leaves are an immediate hit but needle- or narrow-leaved plants are always fighting the "twiggy" or "sticky" tags. It's probably something in the national psyche, all that green bush maybe, otherwise why would we insist on clearing vast areas of what is probably our most useful nursery shrub and nectar provider — manuka — a bottlebrush relative.
Anyhow, back to Callistemon. It is an evergreen genus of around 30 species, mostly medium-sized shrubs with a few prostrate species and small trees, all but four of which are endemic to Australia. They occur over a wide area of Australia but are rarely found in extremely dry places, preferring instead the damp margins of streams and swamps or open forest and woodland.
Those pioneer European botanists, Banks and Solander, found bottlebrushes among the first Australian plants they saw. They collected Callistemon citrinus in 1770 and by 1788 English horticulturists were growing it, along with Callistemon linearis and Callistemon salignus. Callistemon rigidus, Callistemon speciosus, Callistemon rugulosus and Callistemon pallidus soon followed.
Now principally grown as ornamentals, bottlebrushes include a few timber-yielding species among their number. Callistemon citrinus, Callistemon salignus and Callistemon viminalis have fine-grained reddish wood that is very attractive when highly polished. Although unlikely to provide enough timber for construction, the wood is very hard and suitable for small implements and tool handles.
The myrtles, the general family to which Callistemon belongs, are widespread in Australia and New Zealand. They include such plants as Eucalyptus, Leptospermum, Metrosideros and Lophomyrtus.
The closest relatives of the bottlebrushes are the paperbarks (Melaleuca), some of which are very hard to distinguish from bottlebrushes, though minor differences in the flowers mark them clearly for botanists and are not hard to spot once you know what to look for. A bottlebrush flower is actually a flower head or inflorescence made up of small flowers with long stamens arranged around a branch. The stamens of Callistemon are generally connected individually but those of Melaleuca are grouped in clusters, often united in a small cup-like structure at the base.
Bottlebrushes flower over a long period, usually reaching a peak in early summer. Provided the winter is not too severe a collection of species should provide flower year-round.
Like those of other members of the myrtle family, bottlebrush flowers are rich in nectar. Bushes in full flower swarm with bees and are very popular with nectar-feeding birds. Geckoes also feed on bottlebrush nectar. Bottlebrushes certainly aren't native but they will attract native wildlife to your garden.
Conspicuous woody seed capsules follow the flowers and in common with other Australian plants adapted to the ravages of bush fires, many species retain their seeds indefinitely until the capsules are broken open by fire or the death of the plant. I find these amazing structures one of the most interesting parts of the plant, but many gardeners can't stand the sight of them. Sure, over several years they can make the plant look very woody, but that's part of what a bottlebrush is. We don't complain when a weeping willow weeps and it's no use moaning because a eucalypt sheds bark. It's just natural. Still, some people also insist on rasping off palm frond bases for aesthetic reasons. Oh well.
Growing bottlebrushes
Bottlebrushes are tough survivors that struggle on even under the worst conditions, which is why they're sometimes used as street trees. However, their very resilience can work against them because when grown under poor conditions they quickly loose foliage and become gnarled, twisted and woody, which doesn't do anything to enhance their popularity or improve their public image.
While bottlebrushes survive, and may even thrive, on neglect they generally look much better if given the care and attention they merit. As is always the case, the key to success is to consider the natural conditions under which a plant thrives and then attempt to emulate or improve on them. Bottlebrushes are Australian plants but that doesn't automatically mean they thrive in poor soil and are extremely drought tolerant. While they can survive for a while without water, the foliage will look much healthier with regular watering and yearly feeding with a general fertiliser. The level of flower production should show a dramatic rise.
If you feel you have to, pruning is the best way to control the formation of the seed capsules. After flowering cut the stems back to just below the spent flowers. This should also help to encourage a densely branched shrub that is slow to develop a heavily wooded trunk. Bear in mind though, that pruning can quickly destroy the shape of weeping bottlebrushes.
Bottlebrushes are relatively free of disease but prone to several pests. Three, scale insects, mites and thrips, usually indicate poor growing conditions. These pests are usually found on plants grown in very dry locations. They rarely attack or badly damage healthy plants but once a plant is infested they can be hard to eradicate and may lead to the spread of other problems such as sooty mould. Improving the growing conditions may lessen the problems or prevent a recurrence, though you'll probably still have to use insecticides to control the initial infestation. A good blast with a jet from the garden hose every few days also helps deter these pests.
Caterpillars, particularly leaf-rollers and tent caterpillars, may occasionally chew the foliage, but unless present in plague proportions they shouldn't cause intolerable damage. Hand removal is often enough to control them.
What's available
Seed merchants specialising in shrubs and trees, such as Dow's of Gisborne, stock most of the species. The seed is easy to raise and is a good way to obtain unusual plants unlikely to be stocked by nurseries and garden centres.
Plants likely to be seen in nurseries include the following:
Callistemon acuminatus
This tall shrub is capable of exceeding 5 m and developing into a small tree. The flowers are crimson with conspicuous golden anthers.
Callistemon brachyandrus
The prickly bottlebrush is distinguished by its needle leaves and somewhat un-bottlebrush-like flowers. The stamens of the flowers are clustered, rather like a melaleuca, and tipped with gold pollen. The effect is more like a pompon than a bottlebrush. It's a small, rather open bush that is probably best grown with bushy grevilleas or other small Australian shrubs rather than among the large bottlebrushes where it could be overpowered.
Callistemon citrinus
The crimson bottlebrush is probably the best known and most widely grown species. It develops into a large, densely branched bush and produces masses of bright red bottlebrushes from mid spring. The new foliage is reddish and very attractive in its own right. It is sometimes known as the lemon bottlebrush because of the scent of its foliage when crushed. Although this led to its botanical name, citrinus, it's a very faint scent. 'Splendens' is the form most commonly grown, and while scarcely different from the species it can be relied upon for a second burst of flower in late summer and autumn. 'Mauve Mist' is a relatively compact hybrid about 1.8m tall and notable for its lilac flowers that age to magenta. The intensity of this colour varies with the season; in good years it borders on pale purple.
Callistemon comboynensis
The cliff bottlebrush is a 1–2m high shrub, often rangy, native to the gorges and rocky stream banks of northern New South Wales. Its deep red, crimson or occasionally pink flowers appear from late summer.
Callistemon macropunctatus
Known as the scarlet bottlebrush, this species develops into a densely foliaged spreading bush with masses of small bright red flowers. Its pink- and cream-flowered forms are probably more common in New Zealand gardens than the true red-flowered species.
Callistemon polandii
Poland's bottlebrush is a low, spreading shrub native to Queensland. It is rather like the popular hybrid 'Little John' but generally harder with perhaps a slightly coarser growth habit. I consider it a more reliable choice than 'Little John' for frost prone areas.
Callistemon pityoides
Formerly known as Callistemon sieberi (a name now used for a different species), the alpine bottlebrush of the Snowy Mountains is one of the hardiest species and thrives in most parts of New Zealand. Its flowers are a soft yellow and are at their best in early to mid summer.
Callistemon salignus
Although known as the willow bottlebrush this species from coastal eastern Australia does not have a very noticeable weeping habit, the name coming instead from the willow-like foliage. A large tree in the wild, it seldom exceeds 6m high in New Zealand gardens. Its flowers are pale yellow to yellow-green or occasionally red. This species is notable for its papery peeling bark and bronze to pink new growth.
Callistemon viminalis
This, the weeping bottlebrush, is another very tough species. It comes coastal Queensland and northern New South Wales and unlike most species it doesn't become crowded with woody seed heads because it sheds its seeds annually. Although capable of growing to over 6m high if left unpruned, don't trim it too heavily or you'll destroy its attractive weeping growth habit. 'Hannah Ray' (sometimes listed under Callistemon citrinus and possibly a hybrid) is a cultivar with relatively small flowers but lots of them.
Callistemon viridiflorus
This small to medium-sized shrub has aromatic foliage and very distinctive yellow-green flowers. It blooms very heavily and the unusual colour always provokes comment — one of those love or loathe it plants.
Callistemon 'Little John'
Heavily promoted in the late 1980s, this low, spreading bush develops into a neat mound of grey-green foliage with vivid red bottlebrushes. The only drawback is that it is quite frost tender. It struggles through here in Christchurch but rarely thrives. In milder climates it is an ideal rockery or tub plant.
Propagation
There's no great secret to propagating bottlebrushes. Most will grow from cuttings and the species may be raised from seed.
Seed
The seed germinates freely with moderate heat and can be sown at any time from mid-spring to mid-autumn. Sometimes it germinates only too well; as a "budding" plant propagator one of my first jobs was sowing Callistemon citrinus seed, the damn stuff came up like grass, and being a beginner keen to impress I pricked out the lot. Four years later I was still trying to sell the last plants from that batch of seed.
Removing the seed capsules from the bush causes them to break open provided they are kept warm and dry for a few days. Use capsules that have been on the bush from at least the previous season as the seed in the current season's capsules takes time to ripen. Some species release their seeds when ripe rather than retaining them, so you'll need to be ready to collect the seed as the capsules release it. In neither case does it seem necessary to use any fancy pre-sowing treatment, such as smoking, to improve germination.
Simply sow the seed in trays or pots of finely sieved, well-drained potting mix and cover with a very thin layer of soil. A glass cover with some newspaper for shading will ensure rapid germination, usually within a week to 20 days depending on the species.
Water the seed by soaking the seed tray from below. The seeds are quite fine and overhead watering will wash them around in the tray. The young seedlings are very tough and may be watered from above. They can be pricked out into small individual pots as soon as their first true leaves develop.
Cuttings
Cuttings of non-flowering side shoots or growing tips strike well provided they are slightly hardened when taken. The very soft tip growth rots easily and the hard brown wood may never strike. A firm but pliable red or green barked stem around 100–150 mm works best. Use a rooting hormone and if possible strike the cutting under mist, though even relatively primitive methods should yield a strike rate of at least 40%.
Copyright Geoff Bryant
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