You probably think you've covered all your bases: your NPK is on point, your pH is dialed in, and there isn't a pest in sight. Sounds good, but did you know that plants without Manganese can suffer? FoxFarm Bush Doctor Manganese plays a valuable role in photosynthesis, nitrogen assimilation, and helping plants hold their own against environmental stresses. Prepare Your Plants To PERFORM! OMRI Listed and CDFA Registered for Organic Gardening.