Drainage Percentage
The percentage of irrigation volume that drains from the substrate. It is used to manage salt balance, moisture levels, and irrigation strategy.
Drainage percentage is the share of irrigation water that leaves the container, slab, or grow bag as runoff. It is calculated as drainage volume divided by irrigation volume, multiplied by 100.
Drainage percentage = runoff volume / irrigation volume x 100
In indoor growing, drainage percentage helps manage the balance between water supply, nutrient concentration, oxygen in the root zone, and salt accumulation. Too little drainage can allow EC to climb in the substrate. Too much drainage can waste nutrient solution, reduce control, and keep the substrate wetter than intended.
Typical goals vary by system:
- Low-drain strategies aim to reduce waste and rely on careful EC tracking
- Run-to-waste substrates often use controlled drainage to manage salt buildup
- Recirculating systems focus more on reservoir balance than discarded runoff
Drainage percentage should be evaluated with runoff EC, runoff pH, substrate dryback, and plant demand. The right target changes with crop size, light intensity, temperature, and irrigation frequency.
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