A nutrient deficiency is a condition in which the plant contains too little of an essential element to function normally. It shows as specific symptoms: chlorosis, necrosis, distortion, colour change or stunting, in a pattern that depends on the element and its mobility. Cockson and colleagues, and Llewellyn and colleagues, documented deficiency symptoms specifically in cannabis.
In practice
Diagnose by location first: old leaves suggest a mobile nutrient, new growth an immobile one. Then by pattern: uniform, interveinal, marginal or spotted. Before adding anything, check root-zone pH, EC and runoff, because most "deficiencies" in practice come from pH lockout, root damage, cold or waterlogged media, or antagonism from an excess of another element. A tissue test confirms what symptoms only suggest.
Don't confuse with
- Nutrient toxicity: too much of an element, which can mimic a deficiency of another.
- Pest damage: mites, thrips and pathogens can cause spotting or distortion with no nutrient cause.
- Natural senescence: late-flower fade is expected.
Myth check
"Add more nutrients" is rarely the first fix. Check pH and roots first. See how to diagnose any problem.
A mobile nutrient is one the plant can move from older leaves to new growth, so its deficiency shows first on lower, older leaves: N, P, K, Mg, Cl, Mo.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.EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.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.Nutrient lockout is when plants show deficiency symptoms although nutrients are present, because pH, salt build-up, ion antagonism or damaged roots stop uptake.Overwatering is watering so often that the medium stays saturated, starving roots of oxygen, which causes drooping, slow growth and root disease.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.The programmed ageing and breakdown of leaves and other tissues, in which the plant recycles nutrients (especially nitrogen) from old leaves to developing flowers and seeds.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 tissue test is a lab analysis of dried leaf samples that measures the actual nutrient content of the plant, the most reliable way to confirm a deficiency or toxicity.Nutrient antagonism is when an excess of one element reduces the uptake or use of another, such as high potassium suppressing magnesium and calcium.
