Copper is a micronutrient absorbed as Cu2+. It is part of plastocyanin, which carries electrons in photosynthesis, and of enzymes involved in lignin synthesis and oxidative defence. Plants need very little, and it is largely immobile.
In practice
Deficiency is rare in mineral feeds. When it occurs, new leaves may be dark or bluish, twisted, with wilting or dying tips and weak stems. Toxicity is the more realistic risk: copper pipes, copper-based ionisers, copper fungicide residues or overdosing can damage roots and induce iron deficiency. Hydro feeds usually carry only about 0.03-0.1 mg/L (ppm) Cubeing reviewed.
Don't confuse with
Myth check
Copper is sometimes added to reservoirs as a "root protectant". At the doses that suppress pathogens it can also injure roots; treat claims with caution. See root browning in hydro.
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.The process in chloroplasts that uses light energy to turn carbon dioxide and water into sugars and oxygen; cannabis uses the C3 pathway.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.Iron (Fe) is an immobile micronutrient needed to make chlorophyll and run electron transport; deficiency yellows new leaves between green veins.Zinc (Zn) is a micronutrient needed for auxin production and many enzymes; deficiency gives small, twisted new leaves and shortened internodes.Node stacking describes short internodes, so nodes and bud sites sit close together along a stem, giving dense colas and a compact plant.Heat stress is damage or slowed growth when leaf or canopy temperature rises above what the plant can handle, typically above about 30–32 °C (86–90 °F) in cannabis.Copper sulfate pentahydrate (CuSO4·5H2O), about 25.5% copper, supplies trace copper in micronutrient mixes and is toxic to roots in excess.An immobile nutrient stays where it is first deposited, so its deficiency shows on young leaves and growing tips first: Ca, S, Fe, Mn, B, Cu.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.
