Runoff EC is the electrical conductivity of the drainage from a container, in mS/cm. On its own it says little; its value is the comparison with what went in. It reflects the salt concentration in the medium's pore water, which is what the roots actually sit in.
In practice
Rules of thumb for coco and soilless mediabeing reviewed:
| Runoff vs input |
Meaning |
| Within about ±0.3 mS/cm |
Balanced feeding |
| Runoff higher by 0.5–1.0+ mS/cm |
Salts accumulating; increase runoff or lower input EC |
| Runoff lower |
Plant is using nutrients faster than supplied; feed slightly stronger |
Example: input 1.6 mS/cm, runoff 2.8 mS/cm. Salts are building up in the medium. Increase runoff fraction for a few irrigations or do a root-zone flush with a mild nutrient solution, then check that runoff returns towards input.
In drain-to-waste crop steering, growers sometimes let substrate EC climb on purpose to steer generative growth; that is a managed strategy, not neglect.
Don't confuse with
- Input EC: the strength of the solution you apply.
- Substrate EC: measured in the medium by a probe; related but read differently.
Myth check
GenetixBay house position: a root-zone flush to wash accumulated salts out of the medium is the one valid flush. It treats the medium, not the plant, and can be done at any stage. A pre-harvest flush is a Myth and actively harmful: it starves the plant while it is packing on its final weight and resin. See the flush debate.
EC (electrical conductivity) measures how well a solution conducts electricity, a proxy for total dissolved salts; growers read it in mS/cm to gauge nutrient strength.Runoff is the water or nutrient solution that drains out of the bottom of a container after irrigation; growers test it to see what is happening in the root zone.mS/cm (millisiemens per centimetre) is the standard unit of EC for nutrient solutions; 1 mS/cm equals 1 dS/m and 1,000 µS/cm.A soilless medium contains no mineral soil, such as peat, coco, rockwool or perlite blends, and relies mostly on the grower to supply nutrients.Running a large volume of low-EC water or mild solution through the medium to wash out accumulated salts; it treats the medium, not the plant, and suits any stage.Drain-to-waste fertigation feeds each plant fresh nutrient solution and lets the runoff leave the system rather than returning it to the reservoir.Input EC is the electrical conductivity of the nutrient solution going into the pot or system, in mS/cm, including the base EC of the source water.Feeding only plain water for days or weeks before harvest to "clean" the plant; GenetixBay rates it a Myth that harms yield, unlike a root-zone salt flush.Salt build-up is the accumulation of unused fertiliser and water salts in the growing medium, raising root-zone EC and causing osmotic stress and lockout-type symptoms.Osmotic stress occurs when root-zone salt concentration is so high that roots struggle to draw in water, slowing growth and burning leaf tips even in wet media.
