Cannabis pH runoff answer
Runoff pH is the pH of water that drains from the pot after you water. It estimates the pH near the roots. Input pH is what you pour in. A gap between input and runoff points to a root zone shift. Measure runoff with a calibrated pH meter. Collect 10% to 20% of the water volume you added. Test within 5 minutes.
Target pH by medium
- Soil: input 6.0 to 7.0. Runoff 6.0 to 7.0.
- Coco coir: input 5.8 to 6.2. Runoff 5.5 to 6.5.
- Hydro and peat: input 5.5 to 6.0. Runoff 5.5 to 6.5.
Runoff reads high in soil if the meter is off. Calibrate with pH 7.0 and pH 4.0 solutions. Store the probe in KCl storage solution. A dry probe reads low by 0.5 to 1.0 pH.
Why runoff pH drifts
Microbes break down organic matter. This releases acids. Roots release H+ ions when they take up ammonium. This drops pH. Roots release OH- ions when they take up nitrate. This raises pH. High EC salts build up in the medium. This pulls pH down or up. Dry pots concentrate salts. This changes runoff readings. Tap water alkalinity above 120 ppm CaCO3 pushes pH up.
Cannabis PH Water: The Ultimate Guide
Slurry test for soil
Runoff from soil can mislead. Use a slurry test. Take 1 part soil from 2 inches deep. Add 1 part distilled water. Stir for 10 seconds. Wait 15 minutes. Measure the water. Soil pH 6.0 to 7.0 is in range.
What pH Should Cannabis Soil Be?
Fix low runoff pH
- Flush with water at pH 6.5 to 7.0 for soil.
- Use 3 times the pot volume. A 5-gallon pot needs 15 gallons.
- Run the last gallon at the target pH.
- Feed at half strength for 2 waterings.
Fix high runoff pH
- Flush with water at pH 5.5 to 6.0 for coco.
- Check input pH. Lower it by 0.3 to 0.5.
- Add chelated iron if leaves yellow between veins.
When runoff pH does not matter
Runoff pH is a trend tool. One reading is noise. Track input pH, runoff pH, and EC for 3 waterings. If runoff pH stays in range, do not chase a single high or low number. If runoff EC is 0.5 mS/cm above input, flush. For exact crop advice, ask a lab.