N-P-K ratios by growth stage, calcium/magnesium/sulfur deep-dive, organic vs synthetic comparison, top brand analysis, pH stability, and EC/PPM feeding charts.
Nutrients are the fuel of cannabis growth — but more is not more. Cannabis feeding programs require different nutrient ratios at different life stages, precise pH management for nutrient availability, and an understanding of how macro and micronutrients interact. This guide gives you the complete picture from seedling to flush.
Nitrogen (N), Phosphorus (P), and Potassium (K) are the primary macronutrients. Cannabis has dramatically different demands for each element depending on which phase of its life cycle it occupies.
| Growth Stage | N Demand | P Demand | K Demand | Ideal N-P-K Profile |
|---|---|---|---|---|
| Seedling (Week 1–2) | Low | Low | Low | Very diluted (25% strength) |
| Early Veg | High | Medium | Medium | 3-1-2 (N dominant) |
| Late Veg / Pre-Flower | High | Medium-High | Medium-High | 2-2-2 (balanced, transitioning) |
| Early Flower (Week 1–3) | Medium | High | High | 1-3-2 (P and K rising) |
| Peak Flower (Week 3–7) | Low-Medium | Very High | Very High | 0.5-3-3 (PK dominant) |
| Flush (Final 1–2 weeks) | None | None/Trace | None/Trace | Plain water or very light ripening formula |
Cannabis demands calcium, magnesium, and sulfur in quantities approaching those of potassium — hence they are called secondary macronutrients. Many commercially popular grow media (particularly coco coir and soft-water hydroponic setups) are consistently deficient in calcium and magnesium without supplementation.
Calcium provides structural integrity to cell walls and is essential for cell division and root tip development. Unlike most mobile nutrients, calcium is immobile in the plant — deficiencies appear first in new growth (newest leaves). Symptoms: new growth distortion, brown spots on leaves, tip burn. Standard supplementation: 150–200 ppm calcium throughout the entire grow cycle in coco and hydro.
Magnesium is the central atom in the chlorophyll molecule and activates over 300 plant enzymes. Deficiency (interveinal chlorosis — yellowing between leaf veins while veins remain green) typically appears first on middle and lower leaves, as magnesium is mobile and the plant relocates it from older tissue. Supplementation at 50–75 ppm throughout the grow cycle is standard in coco and soft-water setups.
Sulfur is critical for amino acid synthesis, protein construction, and enzyme function. It also plays a role in terpene and secondary metabolite production. Sulfur deficiency resembles nitrogen deficiency but starts on newer growth rather than older. Most complete nutrient formulas include adequate sulfur — deficiency in well-fed plants is uncommon but can occur in heavily flushed hydro systems.
Micronutrients are needed in smaller quantities but are equally essential — deficiency in any micronutrient can significantly reduce yields and plant health. Most quality complete nutrient formulas include a micronutrient blend. pH management is the most common cause of micronutrient lockout.
| Micronutrient | Function | Deficiency Symptom | pH for Availability |
|---|---|---|---|
| Iron (Fe) | Chlorophyll synthesis, enzyme function | New growth yellowing (interveinal) | 5.5–6.2 (locked out above 7.0) |
| Zinc (Zn) | Protein synthesis, internode length | Small leaves, stunted internodes | 5.5–6.5 |
| Manganese (Mn) | Photosynthesis, nitrogen metabolism | Interveinal chlorosis in new growth | 5.5–6.3 |
| Boron (B) | Cell wall formation, pollen viability | Hollow stems, bud abnormalities | 5.5–7.0 |
| Copper (Cu) | Enzyme activation, terpene synthesis | Blue-green leaf discoloration | 5.5–7.0 |
| Molybdenum (Mo) | Nitrogen assimilation | N deficiency-like symptoms | 6.0–7.5 (locked out at low pH) |
| Property | Organic Nutrients | Synthetic Nutrients |
|---|---|---|
| Nutrient release | Slow release (microbially mediated) | Immediate (plant-available) |
| Buffering capacity | High (forgives overfeeding) | Low (precise dosing required) |
| Burn risk | Low | Significant if overdosed |
| Soil biology impact | Highly positive (feeds microbes) | Neutral to negative over time |
| Smell/odor | Can be noticeable | Minimal |
| Flavor profile | Often cited as superior (anecdotal) | Neutral if properly flushed |
| Works in coco/hydro | Difficult (clogs drippers) | Excellent |
| Best medium | Soil, living soil, no-till | Coco, hydro, perlite |
| Brand / Line | Type | pH Stability | Best Medium | Skill Level | Cost |
|---|---|---|---|---|---|
| General Hydroponics Flora Series | Synthetic | Good (manual pH) | Hydro, coco | Intermediate | Medium |
| Advanced Nutrients pH Perfect | Synthetic | Auto-buffered 5.5–6.5 | Hydro, coco | Beginner | High |
| Fox Farm Trio | Semi-organic | Can drift (monitor) | Soil, coco | Beginner–Intermediate | Medium |
| BioBizz Organic Range | Certified organic | Good in soil | Soil, coco (limited) | Beginner–Intermediate | Medium |
| Canna Coco A+B | Synthetic (coco-optimized) | Excellent | Coco specifically | All levels | High |
| Plagron Alga / Terra | Semi-organic | Good | Soil, coco | All levels | Medium |
pH is the master variable in cannabis nutrition. Even a perfectly formulated nutrient solution delivers nothing useful if pH is outside the availability window for each nutrient. The relationship between pH and nutrient availability is non-linear and nutrient-specific.
| Growth Stage | EC (mS/cm) | PPM (500 scale) | PPM (700 scale) | Note |
|---|---|---|---|---|
| Seedling | 0.4–0.8 | 200–400 | 280–560 | Very light; avoid nutrient burn |
| Early Veg | 0.8–1.2 | 400–600 | 560–840 | Start ramping feed strength |
| Late Veg | 1.2–1.6 | 600–800 | 840–1120 | Full feeding program active |
| Early Flower | 1.4–1.8 | 700–900 | 980–1260 | Transition to P-K formula |
| Peak Flower | 1.8–2.2 | 900–1100 | 1260–1540 | Maximum demand period |
| Flush | 0.4–0.8 | 200–400 | 280–560 | Plain water or minimal ripener |
The location of symptoms on the plant is the first diagnostic key — mobile nutrients (N, P, K, Mg) deficiencies appear on older leaves first as the plant relocates them. Immobile nutrients (Ca, Fe, Mn, Zn) deficiencies appear on new growth first.
| Symptom | Most Likely Deficiency | First Response |
|---|---|---|
| Yellowing starts on old leaves | Nitrogen | Check pH first; increase N if pH OK |
| Interveinal chlorosis on old leaves | Magnesium | Foliar spray with Epsom salt (1 tsp/L) |
| Interveinal chlorosis on new leaves | Iron or Manganese | Correct pH to 5.8–6.2 |
| Brown spots on leaves | Calcium | Add CalMag; check for overwatering |
| Brown crispy leaf edges | Potassium or nutrient burn | Check EC; reduce feed if over 2.5 EC |
| Purple stems on new growth | Phosphorus or temperature-related | Check temperature and pH first |
Cannabis in the vegetative stage needs a high-nitrogen formula with a typical N-P-K ratio of 3-1-2 or similar nitrogen-dominant profile. Nitrogen drives leaf and stem growth, chlorophyll production, and overall plant size. A dedicated grow formula is superior to all-purpose fertilizers for veg growth.
During flowering, cannabis shifts to high phosphorus and potassium demand. A flowering ratio of 1-3-2 or 0-3-3 is typical. Nitrogen is reduced but not eliminated — complete nitrogen cutoff in early flower stunts bud development. CalMag supplementation remains important throughout the flowering cycle.
Calcium provides cell wall rigidity and prevents blossom end problems in heavy buds. Magnesium is the central atom in the chlorophyll molecule — a deficiency causes interveinal chlorosis starting on older leaves. Both are commonly deficient in coco coir and soft-water setups without a dedicated CalMag supplement.
For cannabis, the ideal EC ranges are: seedlings at 0.4 to 0.8 EC, vegetative growth at 0.8 to 1.6 EC, and peak flowering at 1.4 to 2.2 EC. These are guidelines — strain and medium adjustments are often needed. Always measure both input and runoff EC to track salt accumulation.