Monopotassium phosphate is the salt KH2PO4, sold as 0-52-34. That analysis is in oxides; the elemental content is about 22.7% P and 28.7% K. It is soluble, slightly acidic and free of nitrogen, sodium and chloride.
In practice
MKP is the usual phosphorus source in mineral feeds and goes in the B stock, apart from concentrated calcium. Many "PK boosters" are mostly MKP. Because cannabis trials show a phosphorus plateau at moderate levels, a small dose is enough. Doubling it adds runoff, not buds.
Units and formula
1 g/L gives about 227 mg/L (ppm) P and 287 mg/L K. Reaching 50 ppm P needs only about 0.22 g/L.
Don't confuse with
- Monoammonium phosphate (MAP): P with ammonium nitrogen instead of potassium.
- Dipotassium phosphate: K2HPO4, more alkaline and with a different ratio.
- Phosphoric acid: a liquid acid that supplies P while lowering pH.
Myth check
MKP is useful, but extra PK in flower does not raise yield past the plateau (Evidence: Established). See bloom boosters.
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.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.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.Monoammonium phosphate (MAP, NH4H2PO4) supplies about 12% nitrogen as ammonium and 26.6% phosphorus, adding P while gently acidifying the root zone.Ammonium (NH4+) is the positively charged form of nitrogen; a small share stabilises root-zone pH, but too much reduces cannabis yield and quality.Phosphate is the ionic form in which plants absorb phosphorus, mainly H2PO4- at the normal root-zone pH of 5.5-6.5.Phosphoric acid (H3PO4) is the most common pH-down acid; it lowers pH while adding phosphorus, about 27% P in the usual 85% grade.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.Phosphorus (P) is a mobile macronutrient used in energy transfer (ATP), DNA and cell membranes; cannabis needs moderate amounts and gains nothing from excess.Potassium (K) is a mobile macronutrient that controls water balance, stomata and enzyme activity; deficiency scorches the edges of older leaves.A bloom booster is a high-phosphorus, high-potassium additive sold for flowering; cannabis trials show a P plateau, so past moderate levels it adds cost and runoff, not yield.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.
