PlantMacronutrient.
A mineral nutrient required in relatively large amounts: nitrogen, phosphorus and potassium (primary) and calcium, magnesium and sulfur (secondary).
What it means for your plants
Nitrogen drives leaf growth, phosphorus supports energy transfer and roots, and potassium regulates water balance and stomata. Calcium and magnesium are often supplied by hard tap water or dolomitic lime in the mix, which is why NPK alone does not describe a complete feed.
IN PRACTICE
Interveinal yellowing on the older leaves of a fertilized plant can point to magnesium, a secondary macronutrient.
Put it into practice
What 10-10-10 or 3-1-2 really means: percent N, P₂O₅ and K₂O by weight, how to convert to elemental nutrients, and why ratio and dilution matter more than size.
NPK numbers explained: what a fertilizer label really tells you
