Ideal NPK Ratios by Stage
| Stage | N | P | K | Focus |
|---|---|---|---|---|
| seedling | 2 | 1 | 2 | Gentle nutrition, root development |
| vegetative | 3 | 1 | 2 | High N for leaf/stem growth |
| flowering | 1 | 3 | 2 | High P for bud/fruit development |
| ripening | 0 | 3 | 3 | No N, P/K for maturation |
Source: General Hydroponics, Canna, Advanced Nutrients consensus ranges.
Frequently Asked Questions
What is the best NPK ratio for vegetative growth?
The ideal NPK ratio for vegetative growth is approximately 3:1:2 (N:P:K). High nitrogen supports rapid leaf and stem development. Phosphorus supports root development, and potassium regulates cell processes and water uptake.
What NPK ratio should I use for flowering?
During flowering, switch to a ratio of approximately 1:3:2. Reducing nitrogen prevents excessive vegetative growth that would divert energy from flower development. Higher phosphorus supports flower and fruit formation.
What does NPK stand for?
NPK stands for Nitrogen (N), Phosphorus (P), and Potassium (K) — the three primary macronutrients that plants require in the largest quantities. The numbers on a fertilizer label (e.g., 10-5-5) represent the percentage by weight of each nutrient.
How do I read NPK numbers on a fertilizer label?
Fertilizer labels show NPK as three numbers: the first is %N (total nitrogen), the second is %P₂O₅ (phosphate), and the third is %K₂O (potash). A 20-10-20 fertilizer contains 20% nitrogen, 10% phosphate, and 20% potash by weight.
Should I flush before harvest?
Many growers reduce or eliminate nutrients (especially nitrogen) in the final 1–2 weeks before harvest, using only water or very low EC solutions. This corresponds to the "ripening" stage with a 0:3:3 ratio or pure water flush. The practice is debated, but reducing nitrogen avoids the "green" taste often associated with high-N residues.