Acacias—commonly known as mimosa or wattle—are beloved for their fragrant yellow flowers and attractive foliage. While mature acacias require little pruning, young plants benefit from careful shaping to ensure they grow into well-structured, healthy trees or multi-stemmed bushes.
When to Prune Acacia
- Prune in mid-spring (April), once the risk of frost has passed. This prevents frost damage to new cuts.
How to Prune Acacia
1. Formative Pruning for Standard Trees
Standard trees have a clear trunk topped with a canopy of branches. Suitable species include Acacia dealbata and A. baileyana.
- Year 1
- Remove all side branches from the lower third of the trunk.
- Shorten side shoots on the middle third of the trunk by half.
- Leave the top third untouched except for removing dead, damaged, or diseased growth.
- Tip: Always cut to an outward-facing bud to encourage branches to grow outward.
- Years 2-3
- Remove the shortened shoots from the lower third entirely.
- Shorten middle-third side shoots by half again.
- Remove crossing or poorly placed branches in the upper third.
- Years 4-5
- Clear the trunk of remaining lower branches to the desired height.
- Thin out crossing, dead, or poorly placed branches in the canopy.
2. Formative Pruning for Multi-Stemmed Bushes
Ideal for vigorous or suckering species such as A. dealbata and A. longifolia:
- Year 1: Cut the main trunk to a height of 8 cm (3 in) above ground. Ensure the cut is smooth to prevent disease.
- Year 2: Choose 3-4 strong, well-spaced stems to keep and cut away the rest.
- Years 3-4: Allow side shoots to grow but remove any that are dragging on the ground, crossing, or misplaced.
3. Caring for Mature Trees
Established acacias need minimal pruning:
- Remove frost-damaged, dead, or diseased branches in mid-spring.
- Cut back flowered side shoots to 2-3 buds below faded flowers.
- Light clipping works for A. cultriformis and A. saligna, which can double as informal hedges.