cannabis ph up ph down dosage
How much pH Up or pH Down to add per gallon of cannabis nutrient solution, when to dose, mixing order, and how to hold a steady root-zone pH.
Short answer: 6.0 to 7.0, target 6.5
Soil pH for cannabis sits between 6.0 and 7.0. Aim for 6.5. That band keeps nitrogen, phosphorus, potassium, calcium, magnesium, iron, and manganese available to the roots at the same time.
Soilless mixes and coco coir run lower: 5.8 to 6.2. Peat-based mixes act closer to soil, so 6.0 to 6.8 fits them.
Why the number matters
pH sets how much of each nutrient stays dissolved in the water around the roots. Move outside the band and parts of the nutrient mix bind to soil particles or fall out of solution.
Cannabis pH Too High: Symptoms, Causes, and Fixes
- Below 6.0: phosphorus, calcium, and magnesium drop. Roots turn brown and leaf tips curl.
- Above 7.0: iron, manganese, zinc, and boron drop. New leaves go pale between green veins.
- Above 7.5: most micronutrients lock. Growth stalls even with full feeding.
How to test the soil
Two tests, two different readings. Know which one you are taking.
- Slurry test: mix equal parts soil and distilled water by volume. Stir, wait 30 minutes, insert a calibrated pH pen. This reads the soil itself.
- Runoff test: water the pot until 10 to 20 percent drains out. Measure the drainage. This reads the root zone plus salt buildup.
A sample from 2 inches down, taken from two or three pots, beats one probe reading. Cheap probe meters drift. A pen with calibration solution holds a reading within 0.1.
How to move the number
Adjust soil before planting when you can. Fix pots slowly, in steps of 0.3 to 0.5 pH, because roots react to swings.
- Raise pH: agricultural lime or dolomite lime. Dolomite adds magnesium with the calcium. Add 1 to 2 tablespoons per gallon of soil and mix through.
- Lower pH: elemental sulfur, or peat, or phosphoric acid in the irrigation water. Sulfur works over weeks, not hours.
- Keep water in range: 6.0 to 7.0 after mixing nutrients. Test the feed, not just the soil.
Root zone pH also moves on its own. Nitrate nitrogen feeding raises it. Ammonium feeding lowers it. Hard tap water pushes it up over a cycle.
Signs you are out of range
Yellow between veins on new growth points up. Dark, spotted older leaves and burnt tips point down. Both look like a feeding problem and often are a pH problem under the surface. Check pH before adding more fertilizer.
Cannabis grows in soil from pH 5.5 to 7.5. It survives outside 6.0 to 7.0. It yields inside it.