Acacia
Young acacia plants require pruning to keep them in shape. Acacia dealbata and A. baileyana can be trained as standards with a 1-2m (3-6ft) trunk, or allowed to reach tree-like proportions. Alternatively, create a wall-trained specimen by cutting back young plants by two-thirds in mid- to late spring. This forms a multi-stemmed bush that can be tied into a support.
Frost-damaged growth should be removed from Acacia planted outdoors in late spring. At the same time cut back sideshoots to two or three buds beyond the faded flowers and, where necessary, deadhead and thin.
Mature acacias resent hard pruning and cannot be renovated, although suckering species such as A. dealbata may regenerate.
Eucalyptus
In contrast, many Eucalyptus, including E. gunnii and E. dalrympleana, can be pollarded or coppiced in spring to keep plants small and encourage more attractive, juvenile foliage.
If a Eucalyptus tree is desired, train a central leader as the trunk. Then, in future years, lift the canopy by removing lower limbs just as they start to die back. Established trees need little attention, except to remove dead or damaged branches.
Leigh Hunt