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EC (Electrical Conductivity)
Definition: EC, or electrical conductivity, measures how easily an electric current passes through a nutrient solution, which rises as more dissolved fertilizer salts are present. Reported in millisiemens per centimeter (mS/cm), EC gives cannabis growers a reliable reading of feed strength in water, runoff, or hydroponic reservoirs that means the same thing on every meter.
How EC (Electrical Conductivity) works
Pure water barely conducts electricity. Dissolve nutrient salts in it and conductivity climbs, so an EC meter is really a feed-strength gauge. Unlike ppm, which depends on the conversion scale your meter uses, EC readings are directly comparable between brands.
Typical EC ranges
| Stage | EC (mS/cm) |
|---|---|
| Seedlings and clones | 0.4 to 0.8 |
| Early veg | 0.8 to 1.3 |
| Late veg | 1.2 to 1.6 |
| Peak flower | 1.4 to 2.2 |
These ranges fit coco coir and hydro. Soil growers usually feed lighter, and strains differ, so treat them as starting points.
Start with your water
Measure plain tap water first. Many US municipal supplies read 0.1 to 0.5 mS/cm before you add anything. Subtract that baseline mentally when comparing to a feed chart, especially if your water is hard.
Reading runoff
Compare the EC of the water you pour in with the runoff that drains out. Runoff much higher than input means salts are accumulating in the medium; water a bit more heavily or lower your feed. Runoff far lower than input suggests the plant is hungry and using everything you give it. Persistently high EC is a common road to nutrient burn.
Keeping your meter honest
Calibrate monthly with a 1.413 mS/cm standard solution, and rinse the probe after each use. Most meters compensate for temperature to a reference of 77°F (25°C).