My first grow I vegged for 6 weeks and the plants were almost 6 ft tall, which sucked as I had no room for the light. This time I vegged for 18 days and at 4 weeks 12-12 they are 1 1/2 - 3 feet which is much better. I now think I vegged a bit early as it took them too long to show sex... 30 days would have been perfect.