NPK for Cannabis: Complete Guide to Macro & Micro Nutrients

AZ_Growshop_Asia · July 25, 2026, 6:26am

ASIANNABIS COMMUNITY

Fertilizers • Article 19

NPK For Cannabis:

Complete Guide to Macro & Micro Nutrients

Updated: July 2026

Data from 20+ peer-reviewed scientific studies (2024-2026)

Compiled by Asiannabis Community

Reference: Viet Growers Community (2015). Viet Grower Handbook

TABLE OF CONTENTS

Primary Macronutrients: N, P, K — Role of Each Element
NPK Ratios by Growth Stage
Secondary Macronutrients: Ca, Mg, S
Micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl
Mobile vs Immobile — Diagnosing Deficiencies
Weekly Nutrient Requirements
Lockout & Interactions Between Elements
Quick Reference Table for Deficiency/Excess

1. Primary Macronutrients: N, P, K

1.1 Nitrogen (N)

Role: Building proteins, enzymes, chlorophyll, amino acids. Most needed during the veg stage.

N deficiency: Uniform yellowing of lower leaves (chlorosis), slow growth, thin stems
N excess: Abnormally dark green leaves, “claw” (curling downward), prolonged veg, reduced flowering
Uptake forms: NH4+ (ammonium) and NO3- (nitrate) — cannabis prefers NO3-

1.2 Phosphorus (P)

Role: ATP (energy), DNA/RNA, root development, flowering and seed production.

P deficiency: Lower leaves turn purple/red, poor roots, small flowers
P excess: Locks out Zn, Fe, Ca — symptoms of these deficiencies
Note: Cannabis does not need as much P as many people think — a study in Frontiers in Plant Science (Bernstein 2021) shows that moderate P levels are sufficient

1.3 Potassium (K)

Role: Stomatal regulation, water and nutrient transport, photosynthetic intensity, resin production.

K deficiency: Brown burnt leaf margins (necrosis), weak plant, loose flowers
K excess: Locks out Ca and Mg
Most needed during late flowering (ripening)

2. NPK Ratios By Growth Stage

Latest research (PMC 2024, transpiration-driven mass-balance): Cannabis absorbs N at 78-155 mg/L, P at 13-49 mg/L, K at 111-216 mg/L during veg — the actual ratio is closer to N:P:K = 3:1:4 (not 3:1:2 as commonly assumed).

Table 1: Recommended NPK Ratios by Growth Stage

Stage	N	P	K	N (mg/L)	EC (mS/cm)
Seedling/Clone	1	0.5	1	80-100	0.4-0.8
Early Veg	3	1	2	120-140	0.8-1.2
Late Veg	3	1	3-4	140-160	1.2-1.8
Transition (W1-2)	2	1.5	3	120-140	1.2-1.6
Early Flower (W3-4)	1.5	2	3	100-120	1.4-1.8
Mid Flower (W5-6)	1	2	3	80-100	1.6-2.0
Late Flower (W7-8)	0.5	1.5	3	60-80	1.2-1.6
Ripening/Flush	0	0.5	1	0-40	0.2-0.6

Sources: Bernstein et al. (2021, Frontiers), PMC transpiration study (2024), Allred & Bugbee (2025).

3. Secondary Macronutrients: Ca, Mg, S

3.1 Calcium (Ca)

Role: Cell wall structure, signal transduction
Deficiency: Brown spots on new leaves, deformed tips, short roots
Cannabis needs 100-200 mg/L Ca in solution

3.2 Magnesium (Mg)

Role: Core of the chlorophyll molecule, enzyme activation
Deficiency: Interveinal chlorosis starting from the middle leaves upward — veins remain green
Sources: Epsom salt (MgSO4), CalMag, dolomite lime

3.3 Sulfur (S)

Role: Protein synthesis, terpenes (thiol structures), enzymes
Deficiency: Uniform yellowing of new leaves (similar to N deficiency but on UPPER leaves)
Rarely deficient when using quality mineral fertilizers

4. Micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl

Table 2: Micronutrients — Roles and Deficiency Symptoms

Element	Main Role	Deficiency Symptom	pH Lockout
Fe (Iron)	Chlorophyll, respiration	Interveinal yellowing of NEW leaves	pH > 6.5
Mn (Manganese)	Photosynthesis, enzymes	Small yellow spots between veins	pH > 6.5
Zn (Zinc)	Hormones, enzymes	Small, deformed, yellow leaves	pH > 7.0 or excess P
Cu (Copper)	Enzymes, lignin	Wilted, purple leaves	pH > 6.5
B (Boron)	Cell walls, cell division	Dead tips, hollow stems	pH > 6.5 or dryness
Mo (Molybdenum)	N fixation, enzymes	Leaf margins curl upward, yellowing	pH < 5.5
Cl (Chlorine)	Osmotic pressure	Wilting, short roots	Rarely deficient

5. Mobile vs Immobile — Diagnosing Deficiencies

This is the most important rule for diagnosing nutrient deficiencies:

Table 3: Mobile vs Immobile Nutrients

Type	Elements	Symptoms Appear On	Why
Mobile	N, P, K, Mg, Zn, Mo	OLD (lower) leaves	Plant transfers these from old leaves to new leaves
Immobile	Ca, Fe, Mn, Cu, B, S	NEW (upper/top) leaves	Plant cannot relocate these elements

Yellowing from bottom to top = mobile nutrient (usually N, Mg, K). Yellowing from top to bottom = immobile nutrient (usually Fe, Ca, Mn).

6. Weekly Nutrient Requirements

The PMC 2024 study (transpiration-driven mass-balance) measured actual cannabis uptake:

N: 78-155 mg/L (varies by strain and stage)
P: 13-49 mg/L (much lower than most feeding charts suggest)
K: 111-216 mg/L (the most heavily absorbed)
Optimal N: ~160 mg/L for both veg and flower (Bernstein 2021)

Note: Many manufacturer feeding charts push P too high during flowering. Sticking closely to research data will save money and avoid lockout.

7. Lockout & Interactions Between Elements

Nutrient lockout occurs when an excess of one element blocks the uptake of another:

Excess P — locks Zn, Fe, Cu
Excess K — locks Ca, Mg
Excess Ca — locks Mg, K
pH too high (> 6.5 soil, > 6.0 hydro) — locks Fe, Mn, Zn, Cu, B
pH too low (< 5.5) — locks Ca, Mg, P, Mo

Solution: Adjust pH to the optimal range (soil 6.0-6.5, coco/hydro 5.5-6.0) BEFORE adding fertilizer.

8. Quick Reference Table For Deficiency/Excess

Table 4: Quick Diagnosis via Leaf Symptoms

Symptom	Location	Possible Cause	Treatment
Uniform yellowing from bottom	Old leaves	N deficiency	Increase N, check pH
Interveinal yellowing, green veins	Mid-old leaves	Mg deficiency	Epsom salt 1g/L
Brown burnt leaf margins	Old leaves	K deficiency or high heat/EC	Increase K, reduce EC
Purple stems/petioles	Whole plant	P deficiency or cold	Check temperature + pH
Yellowing new leaves, green veins	Top	Fe deficiency	pH > 6.5? Lower pH
Brown spots + deformed new leaves	Top	Ca deficiency	CalMag, check pH
Dark green leaves, claw	Whole plant	EXCESS N	Flush, reduce N
Burnt leaf tips	Whole plant	Nutrient burn (high EC)	Flush, reduce EC

References

PMC (2024). “Predicting vegetative phase nutrient uptake in Cannabis sativa L. via transpiration-driven mass-balance.” PMC12872892.
Bernstein N et al. (2021). “Optimisation of Nitrogen, Phosphorus, and Potassium for Soilless Production of Cannabis sativa in the Flowering Stage Using Response Surface Analysis.” Frontiers in Plant Science.
Allred J, Fatzinger B, Bugbee B (2025). “Crop steering through osmotic stress…” Journal of Cannabis Research.
Saloner A, Bernstein N (2020). “Response of Medical Cannabis to Mineral Nutrient Supply.” Frontiers in Plant Science.
Cockson P et al. (2019). “Characterization of Nutrient Disorders of Cannabis sativa.” Applied Sciences (MDPI).
Kalinowski J et al. (2020). “Cannabis Macronutrient Requirements.” J. of Plant Nutrition.
Viet Growers Community (2015). Viet Grower Handbook.

LEGAL DISCLAIMER

The information in this article is for educational and reference purposes only. Growing cannabis must comply with the laws currently in force in your country. In the Kingdom of Thailand, compliance is required with the Controlled Herbs Act B.E. 2568 (2025) and the Ministerial Regulation B.E. 2569 (April 2026). Direct sale, recreational use, and content directed at countries where cannabis is prohibited are all forbidden.

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