Flax/harakeke is not easily compostable, so taking to the Whanganui Resource Recovery Centre as green waste and finding other uses for cut leaves is preferable.
Find a local weaver who will take cut leaves: baskets, mats, string, rope can all be woven or plaited from harakeke.
Harakeke can be cut into 2.5cm bits and used as mulch.
Take to the Whanganui Resource Recovery Centre which can deal with harakeke as green waste.
Please keep from landfill wherever possible.