Cannabis Nutrient Schedule: Week-by-Week Feeding Guide

Why Nutrient Timing Matters

Cannabis has dramatically different nutritional needs depending on its growth stage. Feed the wrong nutrients at the wrong time, and you'll stunt growth, cause deficiencies, or worse — nutrient burn. A well-designed feeding schedule aligned to your plant's actual growth stage is one of the most impactful things you can do for your harvest.

This guide gives you a week-by-week feeding framework for the complete lifecycle — from seedling to harvest. Use it as a starting point and adjust based on your specific genetics, medium, and plant response.

Understanding the Macronutrients

Every nutrient bottle shows an NPK ratio (Nitrogen-Phosphorus-Potassium). Understanding what each does tells you why the schedule looks the way it does:

• Nitrogen (N) — The growth nutrient. Drives leafy, vegetative growth. Cannabis is hungry for N in veg. Too much in flower creates "foxtailing" and harsh smoke. Too little causes yellowing (chlorosis).
• Phosphorus (P) — The root and flower nutrient. Low P needs in seedling/veg, dramatically higher needs as buds develop. Deficiency causes purple stems and slow bud development.
• Potassium (K) — The overall health nutrient. Regulates stomata, strengthens cell walls, enhances resin production. K stays relatively high throughout the grow.

Secondary nutrients (calcium, magnesium, sulfur) and micronutrients (iron, manganese, zinc, etc.) are equally important but needed in smaller amounts. Cal-Mag supplementation is essential for most indoor grows.

Seedling Stage — Weeks 1-2

Nutrients needed: None to minimal

The cotyledons (first round leaves) contain all the nutrition a seedling needs for its first 1-2 weeks. Adding nutrients at this stage almost always causes fertilizer burn on the delicate roots. Use plain pH-adjusted water (6.0-7.0 for soil) for the first 10-14 days.

At week 2, if your seedling has developed its second set of true leaves, you can introduce nutrients at 25% strength. Look for a formula with an N-heavy ratio like 3-1-2 or similar.

Early Vegetative Stage — Weeks 3-4

NPK Target: High N, low P, medium K (e.g., 3-1-2)

Your plant is building roots, stems, and leaves. Nitrogen is the priority. Feed 2-3x per week at 50% of manufacturer's recommended dose, gradually increasing to 75% by week 4. Monitor leaves for any signs of nutrient burn (brown, crispy tips) and back off if you see it.

Target EC: 0.8-1.2 mS/cm for soil. pH: 6.3-6.8 for soil, 5.8-6.2 for coco/hydro.

Late Vegetative Stage — Weeks 5-8

NPK Target: Full N, moderate P, high K (e.g., 5-2-4)

By week 5, your plant should be robustly growing. This is peak vegetative feeding — full nitrogen doses, increasing potassium for structural strength. If you're growing photos (non-autoflowering), this is when you'll flip to 12/12 light schedule to induce flowering.

At week 7-8 before flipping, many growers do a "transition feed" — slightly reduce N, increase P and K to prepare the plant for flowering. Target EC: 1.2-1.8 mS/cm.

Early Flowering — Weeks 1-3 of Flower

NPK Target: Reduced N, rising P, high K (e.g., 2-3-4)

After flipping to 12/12, your plant will enter the "stretch" phase — rapid vertical growth over 1-3 weeks before buds begin forming. Reduce nitrogen gradually. The old rule is "never let nitrogen drop to zero" — a slight presence through mid-flower is fine and prevents premature yellowing.

Introduce a bloom booster (high P/K) to your feeding schedule. Brands like Bud Candy, Big Bud (Advanced Nutrients) or Pure Blend Pro Bloom (General Hydroponics) work well. Continue Cal-Mag at moderate doses.

Mid-Flowering — Weeks 4-7 of Flower

NPK Target: Minimal N, high P, high K (e.g., 1-5-6)

This is peak flowering — buds are swelling, resin glands are forming, and terpene profiles are developing. Your plant needs maximum P and K support right now. Reduce nitrogen to trace amounts.

Watch for deficiencies carefully during this stage. Calcium deficiency (brown spots, curling leaves) and magnesium deficiency (interveinal chlorosis) are the most common mid-flower issues. Maintain Cal-Mag throughout. Target EC: 1.6-2.2 mS/cm.

Add a potassium silicate supplement if available — it significantly strengthens cell walls, improves heat tolerance, and enhances terpene production.

Late Flowering — Weeks 8-10 of Flower

NPK Target: No N, minimal P, moderate K (e.g., 0-2-4)

As you approach harvest, begin tapering down feeding intensity. Reduce all nutrient doses by 50% in the final 2 weeks of feeding. Your plant will naturally start pulling nutrients from leaves (causing yellowing — this is normal and desirable at this stage).

Some growers stop feeding nutrients entirely 1-2 weeks before the flush, relying only on the nutrients already in the growing medium. Monitor trichomes with a jeweler's loupe during this period — you're watching for the shift from clear to milky/amber.

The Flush — Final 7-14 Days

Nutrients: Plain pH-adjusted water only

Flushing involves feeding only pH-adjusted water in the final days before harvest. The goal is to clear residual nutrient salts from the growing medium and plant tissue, resulting in smoother, cleaner-tasting final product.

For soil: flush 7-10 days before harvest. For coco/hydro: 5-7 days is sufficient (lower buffering capacity means nutrients clear faster). Use 2-3x the pot volume in water for a proper flush (e.g., 10-15 gallons for a 5-gallon pot).

Signs Your Feeding Is Right

• Deep green leaves without spots, mottling, or unusual coloring
• Strong stems that support the plant's weight
• Vigorous growth — new leaf and bud development every few days
• Healthy root system (white and odorless if visible)
• Strong aroma developing in flower (terpene production is a sign of health)

Common Feeding Mistakes

• Overfeeding — The #1 beginner mistake. Always start at 25-50% of recommended dose. More is NOT better.
• Skipping pH checks — A perfectly mixed nutrient solution at wrong pH is useless. Always pH after mixing.
• Inconsistent schedule — Feed on a consistent schedule and monitor runoff pH/EC to track root zone conditions.
• Ignoring Cal-Mag — Most reverse osmosis water and indoor grows need supplemental calcium and magnesium. It's cheap insurance.

Putting It Together

The nutrient schedule outlined above is a framework — real growing requires observation and adjustment. Keep a grow journal (our free Beginner's Grow Journal is perfect for this) and note what you feed, at what dose, and how plants respond. Within 2-3 grows, you'll have a dialed-in feeding protocol specific to your strain, medium, and grow style.

Use our Nutrient Calculator tool to get specific ml-per-gallon recommendations for any growth stage.