Callistemons are commonly known as "bottlebrushes" because of the cylindrical, brush-like shape of the flower spike.

Callistemon

Callistemon (bottlebrushes) are members of the genus Callistemon and belong to the family Myrtaceae. They are closely related to paperbark melaleucas, which also have 'bottlebrush' shaped flower spikes. It is difficult to tell to which genus some species belong. Botanists are currently closely studying these plants to determine how they are best classified.

Most Bottlebrushes occur in the east and south-east of Australia. Two species occur in the south-west of Western Australia and four species in New Caledonia. Bottlebrushes can be found growing from Australia's tropical north to the temperate south. They often grow in damp or wet conditions such as along creek beds or in areas which are prone to floods.

Description

The flower spikes of bottlebrushes form in spring and summer and are made up of a number of individual flowers. The pollen of the flower forms on the tip of a long coloured stalk called a filament. It is these filaments which give the flower spike its colour and distinctive 'bottlebrush' shape. The filaments are usually yellow or red, sometimes the pollen also adds a bright yellow flush to the flower spikes. [drawing]
Each flower produces a small woody fruit containing hundreds of tiny seeds. These fruits form in clusters along the stem, and are usually held on the plant for many years. The seeds are usually not released from the fruits for several years, but in some species the fruits open after about a year. Fire also stimulates the opening of the fruits in some bottlebrushes.
The new leaves of many bottlebrushes are very ornamental. The leaves are often coloured and, in some species, they are covered with fine, soft hairs.

Most callistemons are small to medium shrubs but some are prostrate and a few can become small to medium sized trees.

Propagation

Callistemons can be propagated by either seed or cuttings. However, to maintain desirable characteristics of a particular plant vegetative propagation (e.g.. cuttings) must be used. This also applies to propagation of named cultivars.

Seed:

In the case of species which retain the seed indefinitely on the plant, the capsules need to collected and placed in an open container in a warm position until the fine seed is released. This should occur in 2-3 days. For best results, the capsules should be at least 12 month's old (i.e.. the most recently formed capsules are best avoided). With those species which release the ripe seed annually, the plant needs to be kept under observation and seed capsules collected when the capsules commence to open.

Germination of the seed of Callistemon species is usually quite easy by normal seed raising methods. No special pretreatment is needed. Germination should occur in 14 to 30 days, depending on the species.

Cuttings:

Propagation of callistemons from cuttings is generally a reliable method. Cuttings about 75-100 mm in length with the leaves carefully removed from the lower half to two-thirds seem to be satisfactory. "Wounding" the lower stem by removing a sliver of bark and treating with a "root promoting" hormone both seem to improve the success rate.

Cultivation

Callistemons are so common in cultivation and seem to be present in even the most weed infested and poorly maintained gardens, it could be said that they thrive on neglect. However, that is not quite true. What is true is that many will survive with little or no attention but this is often accompanied by sparse foliage and few flowers. To get the best out of them it is useful to consider the way they grow naturally.

Given that callistemons are usually found on moist sites, it should be no surprise to find that they enjoy a reasonable amount of moisture under garden conditions. This does not mean that they require anything like daily watering...once established, they will grow happily with just the occasional watering to help them through dry periods. A sunny position will usually produce the best flowering but plants will tolerate anything except total shade.

Apart from watering, the main concerns for successful bottlebrush growing are pruning, pest control and fertilizing.

The woody seed capsules that form along the stems after each flowering season can look unsightly particularly as the new capsules follow the previous ones in succession on the same stem. To prevent this, it is usually recommended that plants be pruned annually just behind the spent flowers. This pruning also has the added advantage of stimulating branching leading to a greater profusion of flowers in subsequent years . However, pruning those species which have a weeping growth habit can destroy their shape (e.g.. C.viminalis and its cultivars such as "Hannah Ray" and "Dawson river").

There are several pests which can attack callistemons although healthy plants can usually cope without human intervention. Sawfly larvae are common pests. They are bronzy green in colour with a pointed tail and, because they occur in groups, they can inflict a great deal of damage to the foliage quickly. They are best controlled by physically removing them either by hand (using gloves!) or with a jet of water from a hose.

Scale is another pest that can be removed by a strong jet of water but this may need to be carried out several times. If this is not successful, the traditional treatment with white oil is usually effective.

Another pest that can be troublesome is webbing caterpillar. These grubs more commonly attack related genera such as Melaleuca and Leptospermum but can cause damage to certain callistemons (the cultivar C."Little John" seems particularly prone). Again, a jet of water is effective treatment.

Callistemons are fairly tolerant of fertilisers, unlike some other genera of Australian plants. The use of a slow release fertilizer after flowering will usually be sufficient.