The best time to switch your plants to flowering is when they reach a height of 10 to 15 cm. This usually happens after 2 or 3 weeks of veg growth. However, you can adjust this timing according to your strain and preference. Some growers prefer to switch their plants earlier or later, depending on how much stretch they expect from their strain. The stretch is the amount of growth that occurs after switching to flowering, which can vary from 50% to 200% depending on the strain. You want to avoid having your plants grow too tall or too close to the light source, as this can cause problems such as heat stress or light burn.