EC (electrical conductivity) is the ability of a solution to carry an electric current, which rises with the concentration of dissolved ions. Pure water conducts almost nothing; nutrient salts dissociate into charged ions that conduct. EC tells you the total salt strength of a solution, not which ions are present: a solution of table salt and a balanced nutrient mix can share the same EC.
In practice
Typical working ranges for the input solutionbeing reviewed:
| Stage | EC (mS/cm) |
|---|---|
| Seedlings, clones | 0.4–0.8 |
| Early veg | 0.8–1.2 |
| Late veg | 1.2–1.6 |
| Flower | 1.4–2.2 |
More is not better. Hershkowitz, Westmoreland and Bugbee (2025) found elevated root-zone nutrient concentration did not increase yield or cannabinoids in medical cannabis, while Baas and Wijnen (2023) tested cannabis across EC 1.8–12 mS/cm in rockwool. Too high an EC causes osmotic stress and tip burn. Always note your base water EC; tap water often starts at 0.2–0.8 mS/cm.
Units and formula
1 mS/cm = 1,000 µS/cm = 1 dS/m = 10 CF ≈ 500 ppm (500 scale) ≈ 700 ppm (700 scale). EC rises about 2% per °C, so meters report at 25 °C.
Don't confuse with
- TDS/ppm: a number calculated from EC with a conversion factor; EC is the actual measurement.
- Runoff EC: what leaves the pot, not what goes in.
