What to feed cannabis during flowering
Feed a bloom formula with low nitrogen and higher phosphorus and potassium. A common ratio is 2-8-4 or 1-3-2. Keep nitrogen at half to two thirds of the veg rate. Add calcium and magnesium if the base nutrient lacks them. Target 600 to 1400 ppm (EC 1.2 to 2.0) in soil, and 800 to 1600 ppm (EC 1.6 to 3.0) in coco or hydro. Hold pH at 6.0 to 7.0 in soil and 5.5 to 6.2 in coco and water.
When to Flush Cannabis Before Harvest: A Guide
Convenience shapes the product choice. A one-part bloom powder needs one scoop and one pH check. Two-part sets need more measuring and more bottles on the shelf.
Nutrients the plant needs in flower
- Macronutrients: nitrogen (N), phosphorus (P), potassium (K).
- Secondary: calcium, magnesium, sulfur.
- Micronutrients: iron, manganese, zinc, copper, boron, molybdenum.
Nitrogen drives leaf and stem growth. Phosphorus supports root growth, flower development, and energy transfer. Potassium moves sugars and water and affects bud density and terpene content.
Ratio by week
- Weeks 1 to 2, transition: keep the veg formula at 50 to 70 percent strength, add a bloom booster at half rate.
- Weeks 3 to 6, peak: full bloom rate. N-P-K near 2-8-4 with 1 to 2 mL per L of calmag.
- Weeks 7 to 9, ripening: cut nitrogen further. Some growers run plain water for the last 7 to 14 days.
How much phosphorus
Peer-reviewed trials found modest phosphate demand. Saloner and Bernstein (2020) grew medical cannabis at 5 to 60 mg/L phosphorus. Flower yield rose to about 30 mg/L and flattened after that. Extra P above that level did not add bud weight. High P in late flower can lock out zinc and iron.
Signs of wrong feeding
- Burnt leaf tips and dark waxy leaves: too much N.
- Purple stems with curled leaves: cold root zone or low P.
- Yellow lower leaves at week 5: normal senescence or low N.
- Crisp tips on sugar leaves near harvest: overfeeding.
Convenience products
One-part bloom formulas cover the full range with one scoop. They cost more per gram of N-P-K than two-part sets. Autoflower growers use them to avoid mixing errors. Photoperiod growers with reservoirs use two-part lines for control of each element.
Practical schedule
Mix fresh feed every 3 to 4 days in hydro. Water to 10 to 20 percent runoff in coco or soil. Measure EC of the runoff. If runoff EC runs 0.4 higher than input, cut the strength by 20 percent. Check pH before each feed.