There are two model by-laws that might be used to seek orders to force a clean-up. The latter would apply to the garden. Issue NTCs then seek fines, then seek orders.
10 Preservation of fire safety
The owner or occupier of a lot must not do anything … on the lot or common property that is likely to affect the operation of fire safety devices in the parcel or to reduce the level of fire safety in the lots or common property.
12 Appearance of lot
(1) The owner or occupier of a lot must not, without the prior written approval of the owners corporation, maintain within the lot anything visible from outside the lot that, viewed from outside the lot, is not in keeping with the rest of the building.