[header] How to prune mint [title] Prune mint back by about one third after flowering. [step] Wait to prune mint until after it's fully flowered. Using a pair of shears, cut about one third of the length off the end of each stem. 
Mint is a relatively hearty, fast growing herb, so do not be afraid to prune--your plant will be fine. [substeps] Pruning can actually encourage growth.