Cannabis pH Level Chart: Target Ranges
The target pH is 6.0 to 7.0 in soil, 5.8 to 6.3 in coco and peat mixes, and 5.5 to 6.5 in hydroponics. Most soil growers aim for 6.3 to 6.8. Most hydroponic growers aim for 5.8. Outside those windows, some nutrients stop dissolving or bind to root zone particles. The plant then shows a deficiency even when the feed contains enough of that nutrient.
Target pH by Grow Method
- Soil: 6.0 to 7.0. Best range 6.3 to 6.8.
- Coco coir: 5.8 to 6.3.
- Soilless mix (peat and perlite): 5.8 to 6.3.
- Deep water culture and nutrient film technique: 5.5 to 6.5. Best range 5.8 to 6.0.
- Drip in rockwool: 5.5 to 6.2.
Nutrient Availability in Soil
Uptake changes across the pH scale. These windows come from standard soil chemistry charts.
Cannabis PH Problems and Solutions Guide
- Nitrogen: 6.0 to 8.0
- Phosphorus: 6.5 to 7.5
- Potassium: 6.0 to 7.5
- Calcium: 6.0 to 8.5
- Magnesium: 6.5 to 8.5
- Sulfur: 6.0 to 9.5
- Iron: 4.0 to 6.5
- Manganese: 5.0 to 6.5
- Boron: 5.0 to 7.0
- Copper: 5.0 to 7.0
- Zinc: 5.0 to 7.0
- Molybdenum: 6.5 to 8.5
Above pH 7.0, iron, manganese, boron, copper, and zinc tie up. Below pH 6.0, phosphorus, calcium, and magnesium tie up. Iron stays soluble below pH 6.5 in soil. A plant at pH 7.4 with yellow new growth points to iron lockout, not to a shortage in the bottle.
Nutrient Availability in Hydroponics
In water, every element sits in solution, so the windows are narrower and overlap between pH 5.5 and 6.0. Iron, manganese, zinc, and copper need 5.0 to 6.0. Phosphorus, calcium, and magnesium need 5.5 to 6.5. Molybdenum needs 6.0 to 7.0. A setpoint of 5.8 to 6.0 keeps every element in range at the same time.
Cannabis Soil pH vs Hydro: A Comparison Review
How to Measure
- Calibrate the meter with pH 4.0 and pH 7.0 buffer solutions every 2 to 4 weeks.
- Store the probe in potassium chloride storage solution. Distilled water pulls ions out of the glass bulb.
- Measure the feed after nutrients are mixed, not before. Nutrients drop the pH.
- Wait 10 to 15 minutes after mixing for the reading to settle.
- Read at 25 C. Cold solution reads higher than its true pH.
- Test runoff or the reservoir after 24 hours. Runoff is an indicator, not the root zone value.
How to Adjust
Lower pH with phosphoric acid, nitric acid, or citric acid. Phosphoric acid holds its value in a reservoir for days. Citric acid works in soil but breaks down in water within hours. Raise pH with potassium hydroxide or potassium silicate. Add the adjuster in small amounts, mix, wait 15 minutes, then read again.
Water alkalinity controls how much acid a batch needs. Alkalinity is measured in ppm of calcium carbonate. Water at 50 ppm needs little acid. Water at 200 ppm or more needs a large dose before the pH moves.
pH Drift
In recirculating systems, pH climbs as plants take up water and anions faster than cations. A rise of 0.3 to 0.5 per day is normal. Set the reservoir back to 5.8. Do not chase the number every hour.
Common Errors
- Adjusting pH before nutrients are added.
- Using a meter with a dry probe.
- Adding pH up and pH down in the same batch without mixing between additions.
- Treating soil runoff pH as the root zone pH.
Quick Reference
- Soil: 6.3 to 6.8.
- Coco: 5.8 to 6.3.
- Hydroponics: 5.8 to 6.0.
- Calibrate the meter every 2 to 4 weeks.
- Read at 25 C.