Cannabis nutrient ranges are designed to look complicated: six bottles, a feeding chart with forty cells, and part numbers instead of names. Underneath, it's simple. The plant needs about a dozen elements, three of them in quantity, and the whole job is delivering them at the right strength and the right pH without letting salts pile up — with the emphasis shifting from nitrogen to phosphorus and potassium when it flips to flower. Here's how, from reading a label to a routine that works.
Reading a label: N-P-K
The three numbers on every feed — say 3-1-2 — are the percentages of nitrogen (N), phosphorus (P) and potassium (K):
- Nitrogen builds leaves and stems. Veg food. Too much in flower gives leafy, harsh buds.
- Phosphorus drives root growth and flower formation.
- Potassium runs everything — water movement, sugar transport, bud density — and is used heavily in flower.
So a veg formula is nitrogen-heavy (around 3-1-2) and a bloom formula leans to P and K (1-3-2 or so). Calcium, magnesium, sulfur and the micronutrients are in any decent base feed, listed lower on the label.
You do not need six bottles. A base veg, a base bloom, and cal-mag cover a first grow completely. "Bloom boosters", enzymes and finishers are refinements you can add once you've grown a plant and want to tune something.
Organic or mineral?
| Organic (living soil, amendments, teas) | Mineral / synthetic (salt-based liquids) | |
|---|---|---|
| How it feeds | Soil life releases it slowly | Directly available to roots at once |
| Precision | Low — hard to overdo quickly | High — you set the exact strength |
| Forgiveness | High | Low; mistakes show within days |
| Best medium | Soil | Coco, hydro |
| Measurement | Not essential | pH and EC meters essential |
| Speed and yield | Slower, often smaller | Faster, larger |
| Flavour | Many growers prefer it | Fine when flushed properly |
A good organic potting soil with the plant just watered is the easiest first grow. Mineral feeds in coco give more control and bigger plants once you're measuring. Neither is wrong; they're different amounts of involvement.
The two numbers: pH and EC
pH decides whether roots can take nutrients up. Wrong pH locks nutrients out — the plant shows deficiencies with a full pot. Targets:
- Soil: 6.0–7.0, aiming at 6.3–6.8
- Coco and hydro: 5.5–6.5, aiming at 5.8–6.2
Test the water after adding nutrients (they shift it), adjust with pH up or down, and test the runoff too. Runoff drifting from the input tells you the medium is going out of range.
EC (electrical conductivity) is how much nutrient is in the water — feed strength. PPM meters read the same thing on a different scale; know whether yours is 500 or 700 scale, because charts differ. Cannabis is a heavy feeder, and typical ranges, in EC, including whatever's already in your tap water:
| Stage | EC (mS/cm) | PPM (500 scale) |
|---|---|---|
| Seedlings, clones | 0.4–0.8 | 200–400 |
| Early veg | 0.8–1.2 | 400–600 |
| Late veg | 1.2–1.8 | 600–900 |
| Early to mid flower | 1.6–2.2 | 800–1100 |
| Late flower | 1.2–1.6, tapering | 600–800 |
| Final flush | 0–0.4 | 0–200 |
Starting points, not laws. Sativa-leaning and lighter-feeding strains sit at the bottom of each range; heavy indica-leaning feeders at the top. The plant, not the chart, has the final say.
The dosing rule
Start at a quarter of the label dose. Every chart assumes ideal conditions and a plant at full tilt. Move up by a quarter each week only if the plant is pale and growing well with no burnt tips. Most plants end up happy at half to three-quarters of the label. Overfeeding shows as dark glossy leaves and crispy tips within days; underfeeding shows as slow pale growth over weeks and is trivially fixed. Err under — and go lower in the last weeks of flower, not higher.
The routine, stage by stage
Seedlings (first 2 weeks): plain pH'd water in soil — a good mix has enough in it. In coco, a quarter-strength veg feed with cal-mag from the first week.
Veg (photoperiods: as long as you choose; autos: about 3–4 weeks): veg formula, building to full strength for your plant. In soil, feed every second or third watering with plain water between. In coco, feed every watering to 10–20% runoff.
The flip / early flower (first 2–3 weeks of 12/12): the plant stretches and still wants nitrogen — switch to bloom formula gradually over a week or two rather than overnight.
Mid flower (weeks 3–6): full bloom strength. This is peak feeding; buds are forming and the plant is at its hungriest.
Late flower (weeks 6+): taper down. The plant is finishing, not growing, and excess feed now ends up in the smoke.
The last 1–2 weeks: flush. Plain pH'd water only. Fan leaves will yellow — that's the plant using up what it stored, and it's what you want. The pre-harvest flush is debated, but with mineral feeds it costs nothing and many growers find the result burns cleaner.
Coco always gets cal-mag, at every feed. Coco binds calcium and magnesium and starves the plant of them otherwise.
Water quality
Tap water is fine for most people. Let it stand an hour to gas off chlorine (chloramine won't gas off but is harmless at tap levels). Tap water's own EC — usually 0.2–0.5 — counts toward your total; a reading of 0.3 before you add anything is normal.
Very hard water (over ~0.6 EC) may need less cal-mag; RO water needs it every time because it has nothing in it. Don't add cal-mag and have hard water without checking — excess calcium locks out magnesium and potassium.
Root temperature
Nutrient uptake, phosphorus especially, falls off sharply below about 60 °F at the roots. Plants on a cold garage floor show phosphorus deficiency with a full pot. Keep pots off concrete; a seedling heat mat under them does more than any bottle in winter.
Flushing for salt build-up
Separate from the pre-harvest flush: when runoff EC climbs well above what you're putting in, or after nutrient burn, water with plain pH'd water to heavy runoff, let the pot dry, and resume feeding lower. Watering to 10–20% runoff every time is the habit that stops it happening.
The mistakes
- Following the label dose. Quarter strength first, always.
- Not measuring pH. The single cause of most "mystery" deficiencies.
- Feeding heavy in late flower. It ends up in the buds.
- Switching to bloom overnight at the flip. The stretch still wants nitrogen for two weeks.
- Feeding a wet pot. Water only when the pot is light.
- Coco without cal-mag. Deficiencies are almost guaranteed.
- Fixing three things at once. One change, a week, then judge the new growth.
When a plant does go wrong, Diagnosing nutrient deficiencies walks through reading the leaves.
Shopping list
A base veg feed, a base bloom feed, cal-mag, pH up and down, a pH pen, an EC meter, and a jug for mixing. That's a complete nutrient setup for a first grow. Everything else in the range can wait until you have a reason for it.
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