Best overall: a two-part bloom base nutrient fed at rising strength from week 1 to week 6, then tapered, paired with a phosphorus and potassium (PK) booster during weeks 4 and 5. In practice that means measuring EC or ppm at every feed, holding pH near 6.0 in soil and 5.8 in coco or hydro, and cutting base strength by 20 to 30 percent in the final two weeks before a plain water flush. Growers who want the simplest version run a single-part bloom formula with a calcium and magnesium supplement, while growers chasing weight add a PK booster plus a carbohydrate or amino acid product.
The picks at a glance
- Best overall schedule: two-part bloom base plus a PK booster at weeks 4 and 5. Peak strength lands near 1,000 to 1,400 ppm.
- Best simple schedule: one-part bloom formula plus cal-mag. Fewer bottles, fewer mixing errors, reliable results.
- Best budget schedule: dry salt blends in a 3-2-1 style. Lowest cost per gallon, requires a scale and basic math.
- Best organic schedule: compost tea, bat guano, kelp meal, and a mineral amendment. Slower release, less control over exact ppm.
How does a week-by-week flowering nutrient schedule work?
Flowering cannabis moves through four feeding phases: transition, early bloom, peak bloom, and ripening. Each phase changes both the concentration of nutrients and the nitrogen-to-potassium ratio. The chart below is a starting point, not a fixed rule.
Cannabis Nutrients Schedule Chart: A Guide to Optimal Feeding
- Weeks 1 and 2 (transition and stretch): 700 to 900 ppm. Run bloom base at 50 to 75 percent strength and keep some nitrogen available.
- Weeks 3 and 4 (early bloom): 900 to 1,200 ppm. Full base strength, introduce the PK booster at half rate.
- Weeks 5 and 6 (peak bloom): 1,000 to 1,400 ppm. Full PK booster, maximum demand for potassium and magnesium.
- Weeks 7 and 8 (ripening): 700 to 1,000 ppm. Reduce nitrogen, hold potassium, watch runoff EC for salt buildup.
- Final 7 to 10 days: plain pH-adjusted water only.
Which nutrients actually matter during flowering?
Phosphorus drives energy transfer and flower development, while potassium regulates water movement and sugar transport into buds. Calcium and magnesium keep cell walls and chlorophyll functioning once nitrogen drops, and sulfur supports the terpene and resin pathways. Silica is optional but improves stem strength when buds put on weight late.
Cannabis Nutrients Schedule for Soil: A Comprehensive Guide
Micronutrients matter more than most growers expect at high ppm. Iron, manganese, zinc, and boron lock out fast when pH drifts, so a chelated trace blend is worth the extra bottle.
How do you set ppm, pH, and runoff EC?
Mix nutrients, then measure EC before pH. Adjust pH last, because pH-up and pH-down products shift conductivity slightly. Track runoff EC each week: if runoff reads more than 300 to 400 ppm above the input, salts are accumulating and a mild flush is due.
Water temperature between 65 and 70 degrees F keeps dissolved oxygen high and prevents nutrient precipitation. Never mix calcium and sulfate concentrates directly together.
Should you flush before harvest?
Flushing is common practice but the supporting evidence is thin, and peer-reviewed work has not consistently shown a quality gain from withholding nutrients. Many growers still flush for 7 to 10 days to reduce salt taste and save on nutrients. If you skip it, taper strength instead and monitor runoff.
Which option should you pick?
Choose the two-part bloom base with a PK booster if you want maximum control and are willing to measure ppm weekly. Choose the one-part plus cal-mag schedule if reliability matters more than the last few grams. Either way, the schedule itself, not the label, drives the outcome.