The ACT’s Unit Titles (Management) Act used to have a section that said an Owners Corporation (OC) could exempt itself by special resolution from a maintenance obligation subject to conditions that it would not have a significant adverse effect on the appearance of the common property or safety. That seems to have disappeared but perhaps it is still there and you can find it. Now it seems that a maintenance obligation can only be transferred to individual unit owners in the context of a special privilege rule or a condition associated with a ‘minor use’ and those only pertain to common property.
As the hedge is on the boundary of the ‘nature strip’ and individual units, it is arguably a shared maintenance responsibility between the individual units and the OC.
On the other hand, perhaps the private unit areas go up to the external boundary of the OC and the hedge is inside the private unit areas and just extends to the boundary and not onto the nature strip. If so, the OC could note that the hedge is in the private unit areas and require the 5 unit owners to maintain it, including trimming to prevent it from extending out into the nature strip.
What is the status of the ‘west wing’ fence? Is that also a boundary between individual unit areas and the nature strip? If so, aren’t the hedge and the fence the same? The west wingers have a fence boundary and the east wingers have a hedge boundary. Perhaps the hedge requires regular trimming, which is a regular cost but the fence needs only irregular maintenance but might eventually need replacement. Perhaps both should be a shared individual unit owner and OC cost and things might even up eventually.
If all or nearly all are agreed, I’d suggest that an OC rule be adopted by special resolution at a general meeting and properly registered. I suggest that the rule is written symetrically in that it gives the 5 west units OC permission to erect a fence on their boundary subject to a maintenance requirement on those 5 units while the 5 east units are given permission to install a hedge on their boundary subject to a maintenance requirement on those 5 units. I would include a requirement that the fence for the 5 west units be maintained in a consistent style for all 5 west units and that the hedge for the 5 east units be maintained in a consistent style for all 5 east units. I’d include a stipulation that the OC (in effect the EC) can determine what maintenance is required for the fence and hedge and the OC bill the relevant 5 units for any costs associated with that maintenance.