Cannabis Nutrients – Role, Deficiency Pattern, Overdose, Antagonists, and pH for Each Element

Like every higher plant, cannabis needs fourteen mineral nutrients, plus carbon, hydrogen, and oxygen from air and water. These plant nutrients are chemistry, not a cannabis peculiarity: calcium builds the same cell wall in hemp as in tomatoes, and iron drops out of the nutrient solution at high pH. The table shows for each nutrient what it does, where and how its deficiency starts, what too much does, what blocks it, and what to do first. The sections below explain the connections you need for diagnosis.

The fourteen nutrients at a glance

The plant needs six of them in large amounts, the macronutrients nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur. It needs eight only in traces, the micronutrients iron, manganese, zinc, copper, boron, molybdenum, chlorine, and nickel. A well-supplied leaf contains about 15,000 mg of nitrogen per kilogram of dry matter but only 0.1 mg of molybdenum, and still the plant lacks something without the molybdenum.

Nutrient table

Click a name or “Leaf pattern” for the full description in the article on deficiency and overdose.

Nutrient table
Nutrient	Role	Deficiency: how it develops	Too much	Blocked by	First steps
Macronutrients
Nitrogen	Building block of protein and chlorophyll	starts low Early: plant grows more slowly, lowest leaves evenly pale green, often from the leaflet tips Later: strong yellow climbing tier by tier to mid-plant; red-brown leaf stalks Late: lower leaves fully yellow, then brown, and drop Flowering: lower fan leaves first, then stems and sugar leaves from the bud base Leaf pattern	Early: darker green, lots of leaf mass; roots already grow worse Later: smaller plant, leaves glossy and curled down (“claw”, with high salt content), lower fan leaves die Flowering: leaves at the expense of buds Result: less phosphorus, calcium, magnesium, manganese Ammonium above 30 %: shoot tips curled with brown margins, paling, wilting, root damage Leaf pattern	Soil: strongly acidic or strongly alkaline Root zone: leached	Once or twice 300–400 ppm N from a complete feed with 10 % runoff; ammonium at most 30 %
Phosphorus	Energy carrier of the cell, roots and flowers	starts low Early: plant compact, leaves dark green to bluish green, looks overfed Cool or wet: lower leaves, leaf stalks and stems purple to violet, later bronze Warm: lower leaves pale yellow with olive-green, angular, water-soaked spots Late: large brown areas, leaflets roll upwards Flowering: brown ring around the leaflet, looser buds Leaf pattern	Pattern: none up to 90 mg/L Possible: iron or zinc deficiency in new growth; disputed in cannabis Leaf pattern	Soil: below pH 6 Root zone: cold, wet, diseased roots Solution: precipitates with calcium when concentrated	Raise phosphorus; trials: 15 ppm constant feed, 30 mg/L for 80 % of maximum yield
Potassium	Water balance, stomata, sugar transport	starts low Early: margins of lower leaflets yellow, first at serrations and tips; centre stays green Later: yellow moves between the veins, margin scorches light brown; larger dead spots at the margin; leaves bend down Late: broad dead margins, leaves drop Flowering: dark brown spots along the side veins of upper sugar leaves; fan leaves brown and dry Leaf pattern	Pattern: moderate yellowing of older leaves in flowering Usually: magnesium deficiency low down or calcium deficiency at the top Hint: more potassium in the runoff than in the irrigation solution Leaf pattern	Soil: below pH 6 and between pH 7.6 and 8.4 Antagonists: high magnesium, sodium in the water	Measure EC (salt burn looks similar), then raise potassium; guide 60–120 ppm, K : Ca : Mg 4 : 2 : 1
Calcium	Strength of cell wall and membrane	starts at the top Early: shoot tips stunted, new leaflets narrow and pale at the base Later: yellow-brown spots between the veins, twisted leaves, margins roll down Late: shoot tip dies, many side shoots Flowering: burnt tips on young leaves and buds; in one trial brown spots with a yellow halo low down Leaf pattern	Pattern: none described Result: magnesium deficiency despite feeding; in other plants also boron and potassium deficiency Leaf pattern	Climate: high humidity, low VPD, still air Antagonists: ammonium, high potassium, magnesium, manganese Water and medium: RO water, unbuffered coco; soil below pH 6.5	Check climate, water and antagonists, take a leaf sample; calcium nitrate, air movement, buffer coco
Magnesium	Centre of chlorophyll	starts low Early: yellow net between the veins of lower leaves, from the leaf centre outwards Later: green vein skeleton on yellow, small light brown spots between the veins, climbs to mid-plant Late: margins die, leaves curl Flowering: often only after bloom starts; younger fan leaves and upper sugar leaves, smaller buds Leaf pattern	Vegetative: dead spots on old leaves low on the stem Flowering: leaf tips burn, then yellowing; smaller buds Result: less calcium, potassium, zinc, manganese Leaf pattern	Antagonists: high potassium, calcium, sodium, ammonium Water: soft water in flowering Soil: outside pH 6.5 to 8.5	Epsom salt 2.4 kg per 1000 L with 5–10 % runoff, never mixed with calcium feed; guide 50–75 ppm
Sulphur	Protein building blocks	starts mid-plant Early: recently matured leaves mid-plant pale, from leaflet base to tip; lower leaves stay green Later: whole leaf yellow, moves into new growth, plant grows more slowly Late: very pale yellow, brown scorch spots, woody stems Flowering: youngest sugar leaves yellow, upper fan leaves point steeply up Leaf pattern	Pattern: not described in cannabis Result: above about 300 ppm less boron and molybdenum Leaf pattern	Feed: no sulphate (Cal-Mag with magnesium nitrate, 20-10-20) Medium: rockwool and hydroponics supply none Soil: below pH 6	Check EC (normal: sulphur rather than nitrogen); Epsom salt 2.4 kg per 1000 L; target 50–200 ppm S
Micronutrients
Iron	Chlorophyll and photosynthesis	starts at the top Early: youngest leaves paler, yellowing between the veins from the stalk to the tip Later: pale yellow to white between green veins, upper half affected, lower leaves deep green Late: brown spots, growth stalls Flowering: barely visible, only paler sugar leaves Leaf pattern	Early: bronzing at the tips of lower leaves Later: moves inwards and upwards, leaves die and drop Cause: substrate pH below 5, chelate overdose Leaf pattern	Substrate: pH above about 6.5, hard water (over 120 ppm bicarbonate) Roots: too wet, root rot Antagonists: high phosphorus, manganese, zinc, copper	Lower pH to 5.8–6.2; chelate by pH (EDTA, DTPA, EDDHA from 6.8); let it dry down
Manganese	Water splitting in photosynthesis	starts at the top Early: bright yellow net between the veins at the top and middle, from the midrib; margins and veins dark green Later: net reaches the margin, sharp contrast Late: many small light brown to bronze dots Flowering: no sign in the trial Leaf pattern	Early: margins of lower leaves yellow, from the tips Later: yellow moves to the midrib, margin dies, leaf drop Result: iron deficiency in new growth Leaf pattern	pH: high, soil above 7.5 Antagonists: high iron, potassium, magnesium, nitrogen	Check pH, then manganese chelate; no manganese below pH 5.5 (toxicity)
Zinc	Enzymes, growth hormone for shoot elongation	starts at the top Early: margins of new leaves yellow at the serrations, or pale bands in the lower leaf half Later: light brown margin spots, narrow, strappy, distorted leaves Late: new leaves white, shorter plant with short internodes Flowering: less flower mass Leaf pattern	Pattern: dead leaf tips, roots unchanged Result: less iron in the shoot, fewer cannabinoids Leaf pattern	Antagonists: high phosphorus, copper, potassium, magnesium pH: high	Check phosphorus, then zinc; guide 0.05–0.35 ppm
Copper	Photosynthesis, respiration, lignification	starts at the top Early: very late; new leaves slightly distorted, base narrow and yellowish, sometimes dark bluish green Later: yellowing between the veins from the margin Late: margin bends inwards and down, new growth limp and drooping Leaf pattern	Hemp in hydroponics: yellowing, shoot grows much less Result: iron deficiency; in tomatoes short, brown roots Leaf pattern	Soil: above pH 8 Antagonists: high phosphorus or zinc	Check pH and zinc, then copper; guide 0.1–0.18 ppm
Boron	Cross-linking the cell wall, elongation, flowers	starts at the top Early: shoot tip distorted, yellowing from the tips of new leaves like margin burn Later: kinks and twists, whole leaf rolls down, leaf tips drop Late: upper leaves thick and brittle, shoot tip and root tips die, plant wilts Flowering: smaller buds, top cola can die Leaf pattern	Early: margins of lower leaves yellow Later: brown band grows towards the midrib, whole margin dies Cause: mixing error, misset injector, boron in the water Leaf pattern	Soil: above pH 7.5 Antagonists: high calcium Climate: low transpiration	Leaf sample first, then boron; guide 0.875–1.0 ppm, narrow range
Molybdenum	Processing nitrate	starts low Cannabis: no sign for nine weeks in the trial Hemp guide: like nitrogen deficiency, cupped or rolled leaves, pale spots that break through Leaf pattern	Pattern: not described in cannabis; considered barely toxic Leaf pattern	pH: low, the only micronutrient	Keep pH above 5.5; guide 0.075–0.1 ppm
Chlorine	Cell turgor, photosynthesis	starts at the top Hemp guide: limp shoot tips, yellow and brown spots, cupped young leaves, later bronzing Leaf pattern	Pattern (other crops): leaf tip burns first, then the margin; dry and crispy Leaf pattern	pH: independent	Test water for chloride and sodium, flush if in excess
Nickel	Breaking down urea	not described not described in cannabis Leaf pattern	Pattern (other crops): yellow between the veins of young leaves, short main root, brown root tips	not described	not described

The table shows for each nutrient the course from the first sign to the late stage and what is different in flowering. Every pattern in full detail, with look-alikes and rates, is in the article on nutrient deficiency and overdose.

Bottom, top, or middle

Location on the plant is the first clue. A mobile nutrient is one the plant can withdraw from old leaves and send to new growth. If it is short, the plant strips the lower leaves, and the deficiency shows there first: nitrogen, phosphorus, potassium, and magnesium. An immobile nutrient stays where it was built in; if it is short, the shoot tips and young leaves suffer while everything below stays green: calcium, iron, zinc, copper, and boron, with manganese on upper and middle leaves. Sulphur deficiency starts in the middle of the plant.

In flowering the rule does not always hold. In a flowering trial calcium deficiency started on the large lower leaves and sulphur deficiency on the small leaves in the buds, while iron and manganese deficiency were barely or not at all visible. And towards the end of flowering the plant withdraws nutrients from the old leaves anyway; their yellowing from bottom to top is then ageing, not deficiency.

When one nutrient crowds out another

What growers call lockout is often ion antagonism: a nutrient in excess crowds out another during uptake. You then see a deficiency although the missing nutrient is in the fertiliser. These pairs matter in practice:

Potassium in excess can trigger magnesium or calcium deficiency. In cannabis, more potassium lowered calcium and magnesium in leaves and buds, and zinc, iron, and manganese in the root; one of two cultivars suffered at 240 mg/L, which the researchers explain with this drop.
Calcium in excess suppresses magnesium. In other plants it is also listed as an antagonist of boron, and together with a lot of magnesium it suppressed potassium in greenhouse cucumbers.
Magnesium in excess lowered calcium, potassium, manganese, and zinc in cannabis and slowed growth.
Nitrogen above 160 mg/L lowered calcium, magnesium, manganese, and phosphorus in cannabis. Ammonium suppresses calcium and magnesium.
Phosphorus in excess lowers the uptake of iron, manganese, and zinc in field crops and ornamentals. In cannabis this is not settled: in one trial more phosphorus lowered only zinc in the root, in another zinc rose slightly in the leaf.
Zinc in excess lowered iron in the cannabis shoot. In ornamentals, manganese and copper in excess also trigger iron deficiency, zinc and copper crowd each other out, and a lot of iron suppresses manganese.

A crowding-out only shows in growth when the displaced nutrient is already scarce. The main suspect is therefore a fertiliser that supplies one nutrient far beyond need, such as a high-dose bloom feed rich in potassium or phosphorus.

When pH locks nutrients up

pH describes how acidic a solution is and decides whether a nutrient stays dissolved and therefore within reach of the root. Each medium has its own range:

Soil: about 6 to 7.5. Below pH 6 phosphorus, potassium, and sulphur become scarce, below 6.5 calcium; above 7.5 iron, manganese, and boron, above 8 zinc and copper. Molybdenum is the exception: it becomes scarce at low pH and more available above pH 7.
Peat and coco: in soilless substrates most nutrients are available between pH 5.4 and 6.2; for cannabis the NC State group recommends a substrate pH of 5.8 to 6.2.
Rockwool and hydroponics: 5.5 to 6.5 in the root zone. In the nutrient solution iron, manganese, zinc, and copper precipitate above roughly pH 6 unless they are supplied as a chelate, that is, bound to a molecule that keeps them in solution.

Too low is just as harmful. Geraniums take up too much iron and manganese below pH 5.8; yellow, then brown spots and margins appear on the lower leaves. In cannabis the NC State group warns that below pH 5 too much iron and manganese can be taken up; the lower leaves then turn bronze from the tip. Anyone raising pH with lime adds calcium at the same time. Phosphorus deficiency itself acidifies the root zone, and unbuffered coco binds calcium and magnesium from the nutrient solution.

When too much was given

In cannabis an excess shows as a pattern of its own less often than a deficiency does. Documented are dark green, smaller plants with high nitrogen, and with very heavy feeding also glossy, downward-curling leaves that growers call the “claw”; curled shoot tips with brown margins with too much ammonium; dead spots on old leaves in vegetative growth and tip burn in flowering with too much magnesium; dead leaf tips with too much zinc; and yellow, then brown margins on the lower leaves with too much boron or manganese. More often you see the deficiency of the displaced nutrient. EC measures all salts together: if it climbs too high, the root gets water less easily, young leaves bend down and cup, and the margins of young and lower leaves turn brown and later brittle. How to recognise and fix blockades is covered in the article on deficiency and overdose.

How to proceed

Look: where is the pattern, bottom, top, or middle? What pattern does the leaf show? Are several plants affected in the same way?
Measure: pH and EC at the roots, that is in the runoff, the drain, or the tank. Look at the roots.
Check the fertiliser: does it supply a nutrient in excess that crowds out the missing one?
Only then give more of the missing nutrient, in small steps, and watch the new growth.

How to measure for each growing medium is in the article on nutrient diagnosis by growing medium.