Short answer
Not to start with. Treat a bottle's chart as a ceiling, begin at about half to three-quarters of it, and steer by EC: roughly 0.6–1.0 mS/cm for seedlings, 1.2–1.8 in veg and 1.6–2.2 in flower in coco and hydro, and 0.8–1.6 in soil. Raise strength only when runoff and new growth ask for it. Supported.
Why
Charts are generic. They don't know your water, which may already carry 0.2–0.8 mS/cm, your medium or your cultivar. Full chart strength on top of hard tap water or fertilised soil is a common route to tip burn.
The research backs a moderate feed. In deep-flow hydro, doubling input from 2 to 4 mS/cm raised solution nutrients but not yield or cannabinoids [1]. Elevated phosphorus raised leachate P without improving yield or quality [2].
Charts quoting ppm are ambiguous: the same 1.0 mS/cm reads 500 ppm on one meter and 700 on another [3]. A 700-scale chart followed on a 500-scale meter overfeeds by about 40%.
The numbers
| Stage | Coco / hydro EC (mS/cm) | Soil EC (mS/cm) | ppm500 (coco/hydro) |
|---|---|---|---|
| Seedling, clone | 0.6–1.0 | Water only, weeks 1–4 | 300–500 |
| Veg | 1.2–1.8 | 0.8–1.6 | 600–900 |
| Flower | 1.6–2.2 | 0.8–1.6 | 800–1,100 |
| Late flower | 1.2–1.8 | 0.8–1.6 | 600–900 |
All values are total solution EC, including the water.
What to do
- Measure your water's EC.
- Mix at half to three-quarters of the chart and read the EC.
- Adjust to the stage target above, not the chart's number.
- Check runoff EC; more than ~0.8–1.0 mS/cm above input means back off.
- Step up 0.1–0.2 mS/cm at a time if lower leaves pale early.
Common mistakes
- Running full chart plus every additive in the range.
- Following a ppm chart without knowing its scale.
- Ignoring the EC your tap water already brings.
- Reading dark green, clawed leaves as "healthy and hungry".
Related
- Full article: Building a cannabis feed by stage
- Answers: feed every watering? · TDS vs EC meter
- Articles: EC vs ppm scales · brown, burnt tips
- Terms: nutrient burn · feed chart
