Runoff (or drain-to-waste) refers to the nutrient solution that drains out of a growing medium after each irrigation cycle and is not recirculated. In drain-to-waste hydroponic and coco coir systems, runoff carries away accumulated mineral salts that can build up in the medium over time. Monitoring runoff pH and EC is a diagnostic technique that reveals the actual conditions in the root zone β which can differ significantly from the input solution.
Key Facts
- Drain-to-waste systems use runoff to flush salt build-up β typically 10β20% runoff per irrigation
- Runoff EC higher than input EC indicates salt accumulation in the medium
- Runoff EC lower than input EC indicates the plant is consuming more nutrients than it receives
- Runoff pH outside 5.5β6.5 signals a root zone chemistry problem requiring correction
- Recirculating systems capture and reuse runoff β less waste but requires regular solution changes
- Coco coir growers typically target 20β30% runoff per feeding to maintain a clean root zone