Macronutrients are the essential mineral elements a plant needs in the largest quantities, typically present in dry leaf tissue at 0.1% to several percent. The primary macronutrients are nitrogen (N), phosphorus (P) and potassium (K). Calcium (Ca), magnesium (Mg) and sulfur (S) are also macronutrients, often called secondary nutrients. Carbon, hydrogen and oxygen come from air and water and are not counted as fertiliser nutrients.
In practice
A typical cannabis hydro feed carries macronutrients in the tens to hundreds of mg/L (ppm): roughly 150-200 N, 30-60 P, 150-300 K, 120-200 Ca, 40-70 Mg and 50-100 S, varying with stage and system. Fertiliser labels highlight N-P-K, but Ca, Mg and S shortages cause just as many problems, especially with RO water and coco.
Don't confuse with
- Micronutrient: needed in far smaller amounts, but just as essential.
- Macros in diet slang: protein, fat and carbohydrate, unrelated.
- Importance: "macro" refers to quantity, not to how essential an element is.
Sulfur (S) is a secondary nutrient taken up as sulfate, used in the amino acids cysteine and methionine; deficiency yellows new growth fairly evenly.Secondary nutrients are calcium, magnesium and sulfur: macronutrients needed in substantial amounts but not included in the N-P-K numbers on a label.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.The N-P-K ratio is the three numbers on a fertiliser label giving percent nitrogen, phosphate (P2O5) and potash (K2O) by weight, not elemental P and K.RO water is water stripped of most dissolved salts by reverse osmosis; it has near-zero EC and little buffering, so pH moves easily and Ca and Mg must be added.Coco coir is a growing medium made from processed coconut husk, prized for holding water and air at once; it binds calcium and magnesium unless buffered.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.Nitrogen (N) is the macronutrient plants use most, built into proteins, chlorophyll and nucleic acids; it drives leaf and stem growth and is fully mobile.Potassium (K) is a mobile macronutrient that controls water balance, stomata and enzyme activity; deficiency scorches the edges of older leaves.
