Hi there Sean. It’s a pretty easy job as flax is a very hardy plant. You basically want to cut away all of the flower stalks and any leaves that have browned with sun damage. Follow the leaves to the base of the plant and cut there. I’m sure you already know this but wear gloves when dealing with flax.
From a tikanga Māori perspective, there’s some good information at https://collections.tepapa.govt.nz/topic/3623
For Māori, the fan-shaped harakeke plant represents a whānau (family). This symbolism reflects the importance of the plant in Māori life.
The rito, or inner shoot, is likened to a child and is never removed. A family must protect its offspring if it is to survive.
The awhi rito, or protectors of the rito, stand on each side. They are seen as mātua (parents). Like the rito, they are never harvested.
Only the outer leaves, likened to extended family members, are harvested.
Weavers say a karakia (prayer) before cutting the first blade of harakeke.
They always cut on the diagonal, away from the plant’s heart and from top to bottom. This helps rainwater drain away and prevents the heart from being flooded and dying.
Harvesting is not permitted at night or in rain.