Calcium chloride is a very soluble salt of calcium and chloride. The anhydrous form is about 36% Ca; the more common dihydrate (CaCl2·2H2O) is about 27% Ca and 48% Cl. It is strongly hygroscopic and releases heat as it dissolves.
In practice
Its main use in cannabis feeds is supplying calcium when the grower wants to cut nitrogen, such as during a late-flower N taper, since calcium nitrate brings N along. The trade-off is chloride. Small amounts are harmless, but heavy use raises chloride enough to burn leaf margins. Many growers split the job: calcium chloride for part of the Ca, gypsum or reduced calcium nitrate for the rest. Food-grade or reagent grade avoids the contaminants in de-icing salt.
1 g/L of the dihydrate gives about 273 mg/L (ppm) Ca and 482 mg/L Cl.
Don't confuse with
- Calcium nitrate: the standard calcium source, with nitrogen.
- Road de-icing salt: may be calcium chloride but contains impurities.
- Calcium sulfate (gypsum): low solubility, adds sulfur instead of chloride.
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.Gradually cutting nitrogen in late flower, toward zero near the finish, while still feeding phosphorus, potassium, calcium, magnesium, sulfur and micronutrients; GenetixBay's alternative to flushing.Calcium nitrate is the standard hydroponic calcium source, supplying about 19% calcium and 15.5% nitrogen, mostly as nitrate.Sulfate (SO4 2-) is the form in which plants take up sulfur, delivered mainly by magnesium sulfate and potassium sulfate in mineral feeds.Sulfur (S) is a secondary nutrient taken up as sulfate, used in the amino acids cysteine and methionine; deficiency yellows new growth fairly evenly.Calcium (Ca) is an immobile secondary nutrient that builds cell walls and membranes; it travels only in the transpiration stream, so deficiency appears in new growth.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.
