Zinc sulfate is the salt of zinc and sulfate. The two common forms are the heptahydrate (ZnSO4·7H2O, about 22.7% Zn) and the monohydrate (ZnSO4·H2O, about 35.5% Zn). Which one is in the bag changes the dose by more than half again, so read the label.
In practice
It supplies zinc in DIY micronutrient stocks. Plants need only a fraction of a mg/L (ppm) in solution, so the salt is weighed in milligrams or made into a concentrated stock. Like other unchelated metals, it becomes less available as pH rises and is tied up by high phosphorus. Overdosing is easy with a kitchen scale; a 0.01 g scale or a stock solution is the safe route.
Units and formula
1 mg/L of the heptahydrate gives about 0.23 mg/L (ppm) Zn; 1 mg/L of the monohydrate gives about 0.36 mg/L Zn.
Don't confuse with
- Zinc oxide: insoluble, used in soil blends and sunscreen, not hydro.
- Zinc chelate (Zn-EDTA): stays soluble at higher pH.
Zinc (Zn) is a micronutrient needed for auxin production and many enzymes; deficiency gives small, twisted new leaves and shortened internodes.Sulfate (SO4 2-) is the form in which plants take up sulfur, delivered mainly by magnesium sulfate and potassium sulfate in mineral feeds.A micronutrient is an essential element plants need only in trace amounts, below a few mg/L: iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel.pH measures how acidic or alkaline a solution is on a 0–14 scale; in growing it controls nutrient uptake, with soil best near 6.0–7.0 and hydro 5.5–6.5.A stock solution is a concentrated nutrient mix, often 100x or 200x final strength, diluted into the reservoir; calcium and sulfate/phosphate stocks must stay separate.A chelate is a metal ion held by an organic molecule at several points, keeping micronutrients such as iron, zinc and manganese dissolved and available across a wider pH range.
