Zinc is an important nutrient. The optimal concentration of zinc is several parts per million for best growth. Our native soil has about 3 times that amount. If zinc is too high, growth is inhibited by toxicity. Sensitive plants such as woody plants need plant available zinc below about 30 parts per million. Herbaceous plants need zinc below about 50 parts per million. Excessive zinc causes stunting, dieback and discoloration. High zinc restricts the uptake of potassium and other micronutrients.
Avoid using fertilizers containing zinc such as Miracle Gro, Azomite, Ironite, and enhanced bagged compost products like Bumper Crop.