Cannabis in soil grows best at pH 6.0 to 7.0. Cannabis in hydroponics or coco coir grows best at pH 5.5 to 6.5. A root zone outside those ranges blocks nutrient uptake, even when the nutrient mix is correct. This cannabis pH levels chart lists the target numbers, the lockout signs, and the steps to adjust pH.
how to adjust cannabis ph levels
Cannabis pH chart by grow method
- Soil, potting mix or in-ground: 6.0 to 7.0. Target 6.3 to 6.8.
- Coco coir: 5.8 to 6.3. Target 6.0.
- Hydroponics, DWC, NFT, rockwool: 5.5 to 6.5. Target 5.8 to 6.2.
- Peat-based mixes: 5.8 to 6.4.
- Outdoor field hemp: 6.0 to 7.0.
- Plain water before nutrients are mixed: 6.5 to 7.0 for most municipal supplies.
Why pH controls nutrient uptake
pH sets which minerals stay dissolved in the water around the roots. Iron, manganese, zinc, and copper stay soluble at low pH. Phosphorus, calcium, and magnesium bind and drop out of reach at low pH. At pH above 7.0, iron and manganese precipitate and the plant shows deficiency while the nutrient bottle is full.
best ph level for cannabis soil
Nutrient availability by pH number
- Below 5.5: iron, manganese, and zinc run high. Calcium and magnesium drop.
- 5.5 to 6.5: phosphorus, iron, manganese, and zinc sit in range.
- 6.0 to 7.0: nitrogen, potassium, calcium, and magnesium sit in range.
- Above 7.0: iron, manganese, zinc, copper, and boron fall. Phosphorus binds with calcium.
- Above 7.5: most micronutrients lock out.
How to measure pH
- Digital pen meter: reads to 0.1 pH. Buffer and store the probe.
- Calibrate with pH 4.0 and pH 7.0 solution before each run.
- Test the solution after nutrients are mixed, not before.
- For soil and coco, test runoff or a slurry of 1 part soil to 1 part distilled water.
- Drop kits: color match, accuracy near 0.5 pH. Use for a check, not for dosing.
How to adjust pH
- pH down: phosphoric acid or nitric acid. Citric acid works for small reservoirs and shifts back fast.
- pH up: potassium hydroxide or potassium carbonate.
- Add in small amounts, stir, wait 15 minutes, then retest. pH moves after the acid reacts.
- In soil, lime raises pH and elemental sulfur lowers it. Both take weeks to act.
- Change reservoir water every 7 to 10 days. pH drift of 0.3 to 0.5 per day points to a small reservoir or high plant demand.
Signs of a pH problem
Yellow leaf tips with green veins point to iron or manganese lockout at high pH. Brown spots on middle leaves point to calcium or magnesium lockout at low pH. Curled leaf edges, slow growth, and a stable EC with falling water use also point to pH. Confirm with a meter before adding nutrients.
Hemp and CBD plants
Hemp grown for CBD follows the same ranges as drug-type cannabis. Field hemp yields best in soil at pH 6.0 to 7.0. Pots and greenhouse hemp follow the soil or coco row of the chart. CBD concentrations come from genetics and harvest timing, not from pH. pH only decides whether the plant can reach the nutrients it needs.
Quick answer recap
Soil: 6.3 to 6.8. Coco: 5.8 to 6.3. Hydro: 5.8 to 6.2. Test after mixing, calibrate the meter, and move pH in steps of 0.2 or less.