I haven't used foxfarm newts. Have you looked at a foxfarm nutrient feeding schedule? What I can tell you is if you haven't already started using it is to start out at 25% strength and work your way up. At 3 weeks they might need some. DO check the schedule, some use both at the same time. Some veg in veg and bloom in bloom.Can’t get enough of my girls! LOL. When would it be a good time to start these nutrients? #foxfarm #autoflower #newbie #alwayslearning #alwayslistening