Pick regularly to keep plants compact and ensure they produce lots of fresh new growth. Choose the young, soft shoot tips for the most intense flavour. The more you pick, the more they’ll produce.
When mint finishes flowering in late summer, cut the whole plant down to 5cm (2in) from the base. This will encourage fresh shoots, packed with delicious young leaves that you can start harvesting in a few weeks.
https://www.rhs.org.uk/herbs/mint/grow-your-own
Harvest mint leaves at any size by pinching off stems. For a large harvest, wait until just before the plant blooms, when the flavour is most intense, then cut the whole plant to just above the first or second set of leaves. In the process, you will remove the yellowing lower leaves and promote bushier growth. Three such harvests per season are typical for mint.
https://bonnieplants.com/blogs/how-to-grow/growing-mint
Summary:
- Pinch off whole stems instead of picking individual leaves
- Up to three times per year, it may be beneficial to cut the plant down to 2 inches from its base or just above one or two sets of leaves
- The more you pick mint the more it will grow