Callistemon will tolerate hard pruning so it is possible for you to reshape and restructure your specimen. Any dead or damaged wood can be removed in mid-spring, together with any crossing growth to improve structure. This will also help to encourage new vigorous growth. Any reshaping work should be carried out after the flowers have faded by cutting back shoots that spoil the symmetry of the plant. Myrtus communis , common myrtle can reach a height and spread of up to 3m in 20 years.
Growth rate can also be dependent on the general conditions in which it is grown.
The most favourable condition is a well-drained soil in full sun. Myrtus can also be successfully grown in a pot, but again this may limit its size. Myrtus require little pruning, although they can be trimmed lightly for re-shaping purposes. This should be done in mid to late spring before flowering commences. This plant is only half- hardy and therefore may be susceptible to frost damage.