Extract from an article by Derek Oakley of the Bonsai Workshop, Perth.

The Bottlebrush is a spectacular plant when it is in flower, and as a bonsai it is even more so. To cultivate this native as bonsai is a must, not only because of its flowers, but also because of its speed of growth and its capacity to take pruning and training.

Cultivation

This is relatively easy, as Callistemon tolerate root pruning well. I have even root-pruned a plant when it was in flower with no loss, though that is not the preferred timing. However, when faced with “dig it out today because it will not be there tomorrow”, then you have little choice.

Pruning and Repotting

Pruning should be done after flowering and, to obtain the best results for the next season of flowers, cut back hard behind the seedpods that are left. I prefer to cut before they actually set, as soon as the flower wilts, this is usually late October or early November. Cut back hard and be sure to remove all the crossing branches. They are prolific growers and actually benefit from this pruning. The best time to repot is the same as pruning,repot every two or three years.

Potting Mix

I use the same mix for all my natives. One part of coco peat (coir peat), one part good quality commercial potting mix (as natives like an acid soil, you can use a good Azalea mix), and two parts crushed granite. This mix works very well and I see no reason to change it.

Wiring

Wiring is no problem, but check the plant weekly, as the growth is so quick that wire can soon cut in.

Fertilizing

The Bottlebrush is not fussy about inorganic or organic soils. I have used both with good results. However, I feed little and often, alternating with high nitrogen and high potassium. I also use the home brew recommended by Dorothy and Vita Koreshoff in their book on natives. In addition, I also use Phostrogen and Miracid, which acidifies the soil.

Watering

Callistemon do like water. This is contrary to what many believe about Australian natives. I have found that most natives thrive with regular watering, but remember a free draining mix is always best.

The flowers will wilt quickly if they get wet. I have had the misfortune to lose all the flowers when I had been away and my bonsai babysitter did not realize this and within a week the flowers were all gone.