The fertiliser industry has an interest in making you believe you need a different product for every growth phase. The reality is less exciting: cannabis needs nitrogen, phosphorus, potassium, some trace elements, the right pH and an EC concentration within target range. Everything else is simplification or marketing.
NPK — What the Three Main Nutrients Actually Do
Nitrogen (N) is the building block for amino acids and therefore for all proteins in the plant. Without sufficient nitrogen, the plant cannot synthesise chlorophyll — chlorophyll itself contains four nitrogen atoms in the porphyrin ring. Nitrogen deficiency shows first on lower, older leaves (yellowing from below).
Phosphorus (P) is a central component of ATP — the universal energy carrier of the cell — and of phospholipids that build cell membranes. In the flowering phase, phosphorus demand increases as the plant invests massively in flower formation and terpene synthesis.
Potassium (K) regulates osmosis in stomata guard cells — it directly controls whether stomata are open or closed, influencing transpiration, CO₂ uptake and water balance. Potassium deficiency produces necrosis at leaf margins.
EC and pH as Control Variables
| Phase | N:P:K ratio | EC target (mS/cm) | pH target (soil) | pH target (coco/hydro) |
|---|---|---|---|---|
| Seedling | — | 0.4–0.8 | 6.0–6.5 | 5.8–6.0 |
| Veg early | 3:1:2 | 0.8–1.2 | 6.0–6.5 | 5.8–6.2 |
| Veg late | 3:1:2 | 1.2–1.8 | 6.0–6.5 | 5.8–6.2 |
| Flower early | 1:2:3 | 1.4–2.0 | 6.2–6.8 | 5.8–6.2 |
| Flower late | 0:2:3 | 1.2–1.6 | 6.2–6.8 | 5.8–6.2 |
| Flush | — | 0.2–0.5 | 6.0–6.5 | 5.8–6.0 |