Micronutrients are essential elements required in very small amounts, usually under 0.01% of dry tissue. The accepted list for higher plants is iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), boron (B), molybdenum (Mo), chlorine (Cl) and nickel (Ni). Most work as parts of enzymes or electron carriers, so a shortage halts specific processes rather than general growth.
In practice
In a hydro feed they are dosed in fractions of a mg/L (ppm) to a few mg/L: iron around 1-3, manganese around 0.5-1, and molybdenum as little as 0.03-0.05. Because the windows between deficiency and toxicity are narrow, especially for boron and copper, growers dose micros from a concentrated stock or premix rather than weighing tiny amounts of salt. pH governs micronutrient availability more than anything else: most become less available as pH rises, while molybdenum becomes more available.
Don't confuse with
- Beneficial elements: silicon, sodium, cobalt and selenium help some plants but are not essential.
- Macronutrient: needed in hundreds of times larger amounts.
- Micronised: a particle size, not a nutrient class.
Manganese (Mn) is a micronutrient that splits water in photosynthesis and activates many enzymes; low pH can raise it to toxic levels.Copper (Cu) is a micronutrient used in photosynthetic electron transport and lignin formation; plants need only traces, and excess is toxic to roots.Boron (B) is a micronutrient needed for cell-wall structure and growing tips; the gap between deficient and toxic levels is narrow.Molybdenum (Mo) is the micronutrient needed in the smallest amount; plants need it to convert nitrate into usable nitrogen.A nutrient deficiency is a shortage of an essential element in the plant tissue, causing characteristic symptoms; the cause is often pH or uptake rather than an empty feed.Nutrient toxicity is damage from an excess of an element in the plant, either directly or by blocking uptake of others; boron, manganese, copper and chloride are common culprits.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.A beneficial element is one that improves growth or stress tolerance in some plants without being strictly essential, such as silicon, sodium, cobalt and selenium.A macronutrient is an essential element plants need in large amounts, measured in tens to hundreds of mg/L: nitrogen, phosphorus and potassium, plus calcium, magnesium and sulfur.A chelate is a metal ion held by an organic molecule at several points, keeping micronutrients such as iron, zinc and manganese dissolved and available across a wider pH range.Iron (Fe) is an immobile micronutrient needed to make chlorophyll and run electron transport; deficiency yellows new leaves between green veins.
