Callistemon - 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.

   Pruned bottlebrush plant
   Callistemons usually respond well to severe pruning.
Photo: Brian Walters
 
   Sawfly larvae
   Sawfly larvae on the foliage of Callistemon citrinus.
Photo: Brian Walters

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 fertilising.

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. If a bottlebrush plant has become too large or sparsely branched, it can usually be rejuvinated by severe pruning almost to ground level. The accompanying photo shows a plant of Callistemon 'Captain Cook" producing new foliage after a severe cut back. 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 an exception - they 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 fertiliser after flowering will usually be sufficient.


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