Prune the patchouli early in the growing season after the new buds form. Cut the branches just above the buds using sharp pruning shears.
Pinch back the stems as needed to keep the plant from getting long and straggly. The more you pinch back the new growth, the bushier it will be.
Prune branches that reach maturity 70 to 90 days after planting. Cut them back so that only three healthy buds remain on the branch. This allows the branches to regenerate. Branches are mature when one or two of the lower leaves turn yellow.
Harvest the branches 90 to 100 days after planting as they start to mature. Branches mature at different rates so the process is ongoing.