Here are Upham’s instructions for dividing:
First, remove the leaves, then dig up the entire plant. Shake and wash off as much soil as possible so that the pink buds or “eyes” are visible. Each division should have three to four buds, and you’ll need to use a sharp knife to cut through the tough roots.
Space the plants so that there is at least 2 feet between dwarf types and 4 feet between standard types.
Planting for divisions is the same as for new plants: Make sure the pink buds are about 1 inch below the soil, and no more. As you place soil around the plants, keep firming the soil as you go so that the eye does not sink any lower than 1 inch. Water in well, and continue to water through fall and winter as needed to keep the soil moist.
After the soil freezes – usually sometime in December – add a mulch of straw, leaves, compost or other organic material.