Cannabis pH levels belong between 6.0 and 6.8 in soil and between 5.5 and 6.5 in coco, rockwool, and hydroponic water. Inside that window the plant can pull iron, calcium, magnesium, and phosphorus from your nutrient mix. Outside it, those elements lock out and the plant starves even when the reservoir is full.
The right pH range by medium
- Soil: 6.0 to 6.8, with 6.5 as a practical target.
- Coco coir: 5.8 to 6.2.
- Hydroponics, rockwool, and soilless mixes: 5.5 to 6.5.
- Feed water going in: within 0.2 of the medium target.
Soil buffers pH better than a pot of soilless mix, so a single off reading matters less. Hydro moves fast in both directions. A reservoir that reads 5.4 in the morning can hit 6.8 by evening after the plants drink and the water evaporates.
Cannabis Ph Runoff Guide: What You Need to Know
Why pH matters
pH decides which nutrients dissolve and stay charged in the water around the roots. Above 7.0, iron, manganese, zinc, copper, and boron drop out of reach. Below 6.0, calcium and magnesium uptake falls and phosphorus can bind to the medium. The plant shows damage that looks like a feeding problem, but adding more nutrients at the wrong pH makes lockout worse and can burn the root zone.
what ph should cannabis soil be
How to test cannabis pH
- Calibrate the meter with pH 7.0 and pH 4.0 reference solution.
- Fill a clean cup with 50 ml of reservoir water or pot runoff.
- Rest the probe in the cup and stir for 10 to 15 seconds.
- Wait for the number to hold steady and write it down.
- Rinse the probe with distilled water and store it wet in storage solution.
Test the water going in and the water coming out. A gap wider than 0.5 between the two means the medium is pushing pH away from where you set it, and the medium needs attention, not a bigger dose of nutrients.
How to adjust pH
To raise pH
- Add pH up solution one drop per gallon at a time.
- Stir the reservoir for 30 seconds.
- Re-test after 10 minutes before adding more.
To lower pH
- Add pH down solution one drop per gallon at a time.
- Stir and let the water settle.
- Re-test and repeat in single drops until the reading lands in range.
Set pH after the nutrients are mixed, never before. Most mineral feeds push pH up, so the number you read after mixing is the one that counts. For soil grows, feed at 6.4 to 6.6 and let the medium do the rest.
Signs pH is out of range
- Yellow new growth near the light can point to iron lockout at high pH.
- Brown spots on middle leaves with curled edges often follow calcium and magnesium trouble at low pH.
- Purple stems with stalled growth can mean phosphorus is bound up.
- Dark leaves with burnt tips can signal lockout that people mistake for overfeeding.
Preventing pH drift
- Let tap water sit 24 hours before mixing so chlorine and alkalinity settle.
- Mix nutrients in the order the label lists.
- Check pH daily in a reservoir and every other day for hand watering.
- Change the reservoir every 7 to 10 days.
- Flush the medium with pH-corrected water if runoff stays off target for more than a week.
Plant pH versus body pH
Most pH questions about cannabis are about growing it. The human body holds blood pH inside a tight range on its own, and no food, drink, or flower shifts it. Cannabis purchased from a licensed shop is judged on potency, terpenes, and moisture, not on a pH number.
Quick reference
Soil at 6.5, coco at 6.0, hydro at 5.8. Test before you feed, adjust in small steps, and fix pH before you chase a deficiency with extra nutrients.