Pinching

Removing the growing tip from the laterals or stems of a plant. This encourages the plant to grow two stems where there was one. As a result, there is more new growth and therefore more flowers.Each lateral or stem can be pinched out when it has 2/3 nodes or 10cm long.

Stop pinching
About 8 to 10 weeks before you want the plant to flower. If you keep pinching you will reduce flowering as it is from the growth point that flower buds develop.