Cannabis Nutrient Schedule: Week-by-Week Feeding Chart
Most nutrient companies publish feeding charts that assume perfect water, perfect environment, a maximum-yield strain, and a grower who never watches the plant. Follow those charts literally and you will burn tips by week 3 of flower every single grow. The chart is a starting point. The plant is the source of truth. This guide gives you the numbers to start from, then teaches you the four plant signals that override those numbers.
Why "Follow the Bottle" Fails
Nutrient labels are built around a maximum tolerable dose for a heavy-feeding photoperiod strain in inert coco. Your Northern Lights auto in living soil is not that plant. Overfeeding shows up as tip burn first, then clawed leaves, then salt lockout that mimics deficiency, which panics beginners into feeding more. The cycle ends in a stalled grow at week 5 of flower — exactly when the plant should be swelling the hardest.
The framework this article uses: chart = ceiling, plant = actual demand. Start at 60–70% of the ranges below and only push higher if the plant asks.
Nutrient Demand by Growth Stage
The N-P-K ratios below describe the shape of the feed, not a specific product. EC is measured after mixing at your working pH.
| Stage | Week | N-P-K Ratio | EC Soil | EC Coco/Hydro | Key Focus | Warning Signs |
|---|---|---|---|---|---|---|
| Seedling | 1–2 | 1-0.5-1 | 0.4–0.6 | 0.6–0.8 | Root establishment, plain water OK | Yellow cotyledons = fine; tip burn = too hot |
| Early Veg | 3–4 | 3-1-2 | 0.8–1.2 | 1.0–1.4 | Nitrogen ramp, cal-mag intro | Pale new growth = N low |
| Late Veg | 5–6 | 3-1-3 | 1.2–1.6 | 1.4–1.8 | Root mass, prep for stretch | Dark clawed leaves = N tox |
| Stretch (Flower wk 1–2) | 1–2 | 2-2-3 | 1.4–1.8 | 1.6–2.0 | Transition ratio, cal-mag critical | Purple stems = P/pH |
| Early Flower | 3–4 | 1-3-4 | 1.6–1.8 | 1.8–2.2 | P/K climb, bud initiation | Rusty spots = Ca lock |
| Peak Bloom | 5–6 | 1-3-5 | 1.6–2.0 | 2.0–2.4 | Max K, PK boost window | Interveinal yellow = Mg |
| Late Flower / Ripen | 7–9 | 0-2-4 | 1.2–1.6 | 1.4–1.8 | Taper N, K only | Fade begins — expected |
| Flush | Final 7–10d | Plain water or 0.2–0.4 | 0.0–0.4 | 0.0–0.4 | Runoff clarity | Rapid fade — desired |
A few notes on the table before you use it. EC values assume RO or filtered tap around 0.2–0.3 EC in — subtract your source EC from the target to get the amount of dry nutrient to add. Coco numbers run higher than soil because coco is inert; the entire cation exchange capacity is whatever you put in the reservoir. Hydroponic recirculating systems (DWC, RDWC) sit at the lower end of the coco range because roots contact the solution 24 hours per day, not just at feed time.
The N-P-K ratios listed are the ratio at the root zone, not the ratio printed on your bottle. A 4-0-1 base plus a 1-4-6 bloom mixed 1:1 produces a 2.5-2-3.5 solution — very close to the stretch target above.
Reading Your Plant vs Following The Chart
Four signals override every number in the table:
- Tip burn on the newest fan leaves — back off EC by 20% at the next feed and hold. The plant is telling you the ceiling for this specific plant, this specific week is below the chart. Do not "flush" unless burn is progressing down the leaf. Just feed lighter.
- Pale new growth working up from the middle of the plant — nitrogen is short for the current growth rate. Move up one stage on the chart (early veg → late veg ratio) and re-evaluate in 4–5 days. Do not double the EC.
- Purple stems and petioles combined with slow growth — check root-zone pH first. Soil should read 6.2–6.8 in runoff; coco 5.8–6.2. Below 6.0 in soil locks phosphorus regardless of how much you feed. Fix pH before adding P.
- Dark green, clawed, "over-fed" leaves — nitrogen toxicity or salt buildup. Flush with 3x pot volume of plain pH'd water, then hold at plain water for two feeds. Resume at 50% strength.
Notice what these signals share: the plant tells you before the chart does, and the correction is always small and slow. If you find yourself making 40%+ changes to any parameter more than once per grow, you are chasing the plant instead of reading it.
Organic vs Synthetic Feeding
A synthetic feed like GH Flora, Advanced Nutrients Sensi, or Canna is bioavailable within hours. An EC meter reads the exact salt load in the root zone, and adjustments show up in the plant within one to three days. Living soil is different: the microbial community mineralizes organic matter over days to weeks, and an EC meter reads only the free salts — not the bank of nitrogen tied up in worm castings or bat guano that will release over the next month.
Practical implication: do not use the EC column above for a true living-soil grow. Soil growers on Coot's Mix, Kind Soil, or a similar amended base should focus on the ratio and warning-sign columns and water plain most of the time. Add a compost tea (AACT) every 10–14 days in veg, weekly in early flower, and stop at flower week 5. Top-dress once at transplant, once at pre-flower, and once at flower week 3.
If you are a soil-in-a-bag grower using Fox Farm Ocean Forest or Happy Frog with bottled synthetic nutrients, the EC column applies — you are effectively running a slow hydroponic system.
Schedule by Medium
| Medium | Feed Frequency | EC Upper Limit | pH Target | Key Difference |
|---|---|---|---|---|
| Soil | Feed → water → water | 1.8 | 6.3–6.8 | Buffered, forgiving |
| Coco Coir | Every watering | 2.2 | 5.8–6.2 | Inert, cal-mag mandatory |
| DWC / Hydro | Continuous | 2.0 | 5.5–6.0 | Temp <68°F critical |
| NFT | Continuous flow | 1.8 | 5.6–6.0 | Root film sensitive to spikes |
The feed-water-water rotation for soil exists because organic and amended soils reload their microbial nitrogen banks between feeds. Coco has nothing to reload — every watering must be a feed at target EC, or the plant is on a starvation cycle. In DWC, the reservoir is the root zone, so temperature and dissolved oxygen matter more than EC. Warm nutrient solution (>72°F) drops dissolved oxygen and kills roots long before an EC problem shows up.
Eight Common Mistakes That Ruin Grows
- Chasing the label EC instead of the plant response. The label is a ceiling for a heavy feeder in ideal conditions. Start at 60% and move up only on plant demand.
- Skipping cal-mag in coco or with RO water. Coco strips calcium from solution during buffering, and RO strips it from your tap. Calcium deficiency shows on new growth as brown-spotted, curled leaves. Add cal-mag first every mix.
- Feeding full strength to seedlings. The seed cotyledons carry 10–14 days of nutrients. Full-strength veg feed on a two-week-old seedling burns roots before you see burn on leaves.
- Running the same EC through stretch and peak bloom. Stretch demands N; peak bloom demands K. Same EC, wrong ratio, invisible deficiency.
- Ignoring runoff EC. Input EC minus runoff EC should stay within 0.3. A runoff 0.6 higher than input means salts are accumulating faster than the plant uses them — flush and drop input EC.
- pH-ing before adding cal-mag. Cal-mag drops pH significantly. Adjust pH after the full mix is complete, or you will chase the meter for 20 minutes and still land off target.
- Stacking a PK booster on top of an already high-K bloom base. Most bloom formulas already run 1-3-5 or richer. Adding a 0-9-18 booster on top pushes potassium into toxic territory, which shows as brown crispy tips (mistaken for nitrogen burn and mis-corrected).
- Flushing organic living soil. Flushing floods the soil, kills aerobic microbes, and destroys the biology doing your feeding work. In living soil, "flush" means water plain — never with 3x pot volume of tap water.
Advanced Feed Adjustments: Water Source, Temperature, and Runoff
Three variables that never appear on a nutrient bottle but change the effective feed at the root zone are water source hardness, reservoir temperature, and runoff cadence. Tap water in most US and European cities lands between 0.2 and 0.5 EC before any nutrient is added, and that starting EC counts toward your ceiling. A grower running "1.8 EC feed" from a 0.4 EC tap is actually delivering 1.4 EC of added nutrients — closer to a late-veg feed than the peak-bloom target on the chart. Test your source with the meter you already own; if it reads above 0.3, either subtract that value from the chart target or move to RO water for the flower half of the cycle.
Reservoir and root-zone temperature swing dissolved oxygen and nutrient uptake in equal measure. Above 72°F in DWC or a nutrient-rich soil pot, dissolved oxygen drops below 6 ppm and roots start to brown at the tips within 48 hours. Below 62°F, uptake of phosphorus and potassium slows dramatically — the plant looks P-deficient even though the reservoir is loaded with P. Feed math is only meaningful when the root zone sits in the 65–72°F window; outside it, adjust environment first, EC second.
Runoff cadence matters most in soil and coco. The rule is: input EC and runoff EC should stay within 0.3 of each other over a two-week window. Runoff climbing means salts are accumulating faster than uptake — feed lighter or flush with pH'd plain water at three times pot volume. Runoff falling means the plant is stripping the medium faster than you are replacing — feed heavier or move up a stage on the chart. Never make both changes at once; you will not know which move worked.
What a Well-Dialed Feed Log Looks Like
The single best log a grower can build for their own future reference is a simple per-feed record: date, growth day, stage, input EC, input pH, runoff EC, runoff pH, volume in, volume runoff, and a short free-text note. Fifty entries into a cycle you can graph input EC against runoff EC and see the exact week the plant switched from N-hungry to K-hungry — usually a much cleaner signal than trying to remember what the fan leaves looked like on day 42. Two cycles of the same strain and the graph starts telling you exactly which stage to bump PK and which stage to back off. That per-strain history is worth more than any published chart because it was written by your plants in your environment.
Track Your Feeds with StrainTrakker
The reason this guide keeps repeating "start low, watch the plant" is because the feedback loop is 3–5 days long. You cannot hold that in your head across a 10-week flower cycle for four plants of two different strains. StrainTrakker logs every watering event with input EC, runoff EC, pH in, pH out, volume, and free-text notes. The per-strain graph flags EC creep before you see tip burn — usually a full week ahead of a visible warning sign. Save your best-performing schedules as templates and reuse them on the next run of the same strain instead of starting from a bottle label every cycle. That single habit is the difference between growers who improve every cycle and growers stuck at the same yield for years.