Cannabis pH Up and pH Down Dosage: A Practical Guide
How much pH up or pH down to add to cannabis water, with starting doses per gallon, target ranges for soil, coco, and hydro, and fixes for drift.
Cannabis pH Levels
Cannabis in soil grows best at pH 6.0 to 7.0. Coco and hydroponic systems run lower, at pH 5.5 to 6.5. Root zone pH controls which mineral salts stay dissolved in the water. Wrong pH does not kill a plant fast. It locks out nutrients, so leaves yellow, tips burn, and growth slows while feed sits in the pot unused.
Cannabis pH Up and pH Down Dosage: A Practical Guide
Why pH Matters
Each nutrient dissolves in a narrow window. Calcium and magnesium fall out of solution below pH 5.5. Iron, manganese, zinc, and copper bind up above pH 7.0. Phosphorus narrows above 6.5 in some mixes. A plant can sit in a full-strength nutrient solution and still starve when pH sits outside the window.
Ranges by Growing Medium
- Soil: 6.0 to 7.0. Aim for 6.3 to 6.5 on feed water.
- Coco coir: 5.8 to 6.3.
- Hydroponics, DWC, rockwool: 5.5 to 6.0.
- Living soil with heavy organic matter: 6.5 to 7.0. The mix buffers itself.
How to Measure
Use a digital pen with a glass probe. Calibrate with pH 7.0 and pH 4.0 buffer solution before each run. Store the probe in KCl storage solution, not tap water. pH readings shift with temperature, so read at room temperature. Test feed water after mixing nutrients, not before. Fertilizer salts move pH by 0.3 to 1.0 points.
Runoff and Slurry Tests
For potted plants, pour water until 10 to 20 percent runs out the bottom. Collect the first runoff and read it. Runoff pH of 0.5 points below input can mean salt buildup in the root zone. For a soil slurry test, mix equal parts soil and distilled water, stir, wait 15 minutes, then read the liquid.
optimal ph for cannabis plants
Adjusting pH
pH down uses phosphoric acid, nitric acid, or citric acid. pH up uses potassium hydroxide or potassium silicate. Add drops, stir, wait, and read again. Move in steps of 0.2 points. Citric and other organic acids fade in a reservoir within 24 to 48 hours. Mineral acids hold a set point longer.
Fixes for Common Problems
If pH drifts between reservoir and runoff, check microbial activity and recheck the meter. For soil that reads below 5.5, add dolomite lime at 1 to 2 tablespoons per gallon of medium. For soil above 7.5, mix in elemental sulfur or peat moss. Do not push pH in two directions at once.
What pH Does Not Fix
pH is one variable. Light intensity, EC, water temperature, and root health also change nutrient uptake. A plant at pH 6.2 with an EC of 3.5 shows tip burn from salt, not from pH. A pH reading alone does not diagnose a grow.