Potassium sulfate is the salt of potassium and sulfate. Pure K2SO4 is about 44.9% K and 18.4% S; fertiliser grades are commonly sold as 0-0-50 or 0-0-52 (K2O), roughly 41-43% K. Solubility is lower than most hydro salts, around 110 g/L at room temperaturebeing reviewed, so concentrated stocks are limited.
In practice
It is the go-to salt for raising potassium without raising nitrogen. In per-element feeding, swapping some potassium nitrate for potassium sulfate is how growers taper N in late flower while holding K steady. It belongs in the B stock, away from concentrated calcium, because calcium sulfate precipitates. Use soluble or "greenhouse" grade; agricultural granules can contain insoluble residue.
1 g/L of pure salt gives about 449 mg/L (ppm) K and 184 mg/L S.
Don't confuse with
- Potassium chloride (muriate of potash, MOP): cheaper but adds chloride.
- Potassium nitrate: supplies nitrogen with the potassium.
- Potassium magnesium sulfate (langbeinite): a mixed mineral with Mg too.
Sulfate (SO4 2-) is the form in which plants take up sulfur, delivered mainly by magnesium sulfate and potassium sulfate in mineral feeds.Per-element dosing builds a feed from individual salts or single-element stocks so each nutrient can be set independently, such as cutting nitrogen without cutting potassium.Potassium nitrate (KNO3) is a soluble fertiliser salt supplying about 13% nitrogen as nitrate and 38% potassium, used in both veg and flower feeds.As a plant nutrient, chlorine is used as the chloride ion (Cl-) in tiny amounts for photosynthesis and osmotic balance; excess from water or salts is the usual problem.Magnesium sulfate heptahydrate, sold as Epsom salt, is the common hydro magnesium source, supplying about 9.9% magnesium and 13% sulfur.Potassium (K) is a mobile macronutrient that controls water balance, stomata and enzyme activity; deficiency scorches the edges of older leaves.Sulfur (S) is a secondary nutrient taken up as sulfate, used in the amino acids cysteine and methionine; deficiency yellows new growth fairly evenly.
