Potassium nitrate is a salt of potassium and nitrate, sold as fertiliser grade 13-0-46. That means 13% N and 46% K2O, which is about 38% elemental K. It is fully soluble and contains no chloride or sodium.
In practice
It is the main way to add potassium while also adding nitrogen. It is compatible with calcium nitrate, so it can sit in either the A or the B stock. Shifting part of the potassium from potassium nitrate to potassium sulfate or MKP lowers nitrogen while keeping K steady, which is one way per-element feeds taper N in late flower. Store it away from heat and combustibles, as it is an oxidiser.
Units and formula
1 g/L gives about 130 mg/L (ppm) N and 380 mg/L K.
Don't confuse with
- Potassium sulfate: supplies K and S, no nitrogen.
- Sodium nitrate (Chile saltpetre): brings sodium, not wanted in cannabis feeds.
- Potassium chloride (muriate of potash): brings chloride; avoided in hydro.
Nitrate (NO3-) is the main form of nitrogen in hydroponic and soilless feeds; its uptake tends to push root-zone pH upward.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.Sodium (Na) is not essential for cannabis; it enters through water, softeners and some inputs, and at high levels causes salt stress and crowds out potassium and calcium.Calcium nitrate is the standard hydroponic calcium source, supplying about 19% calcium and 15.5% nitrogen, mostly as nitrate.Potassium sulfate (K2SO4) supplies roughly 41-45% potassium and 17-18% sulfur with no nitrogen, useful for adding K while tapering N in late flower.Monopotassium phosphate (MKP, KH2PO4) supplies about 22.7% phosphorus and 28.7% potassium with no nitrogen, and is the base of most PK boosters.Potassium (K) is a mobile macronutrient that controls water balance, stomata and enzyme activity; deficiency scorches the edges of older leaves.The guaranteed analysis is the legally required label statement of minimum nutrient content, giving P as P2O5 and K as K2O; multiply by 0.436 and 0.830 for elements.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.
