Cannabis needs a root-zone pH of about 6.0 to 6.5 in soil and 5.5 to 6.0 in coco or hydro. Within that range the plant can absorb every nutrient it needs. Outside it, nutrients lock out and cause deficiencies even when they are present in your feed. Test your water and runoff, and correct pH before every feeding.
Why pH controls everything
We run a Colorado nursery, and we would guess half the deficiency photos growers send us are really pH problems in disguise. pH measures how acidic or alkaline your water and root zone are on a scale of 0 to 14. Each nutrient has a pH band where roots can take it up. Drift out of range and iron, calcium, magnesium, or phosphorus become chemically unavailable, so the plant starves in a full tank. Fix pH first, before you ever add more nutrients.
Target pH by medium
The right range depends on what you grow in. Soil buffers itself and sits higher; soilless media like coco and hydro run lower because you control the whole nutrient solution. Here are the ranges we hold to.
| Medium | Target pH range | Sweet spot |
|---|---|---|
| Soil | 6.0 to 7.0 | 6.3 to 6.5 |
| Coco coir | 5.5 to 6.3 | 5.8 to 6.0 |
| Hydroponics | 5.5 to 6.0 | 5.6 to 5.8 |
A useful trick in soilless setups is to gently vary within the range across feedings, which helps different nutrients stay available. In soil you can hold steady around 6.3 to 6.5. Freshly rooted clones going into soil are happiest around 6.0 to 6.5, and into coco around 5.5 to 6.0.
How to test and adjust
Buy a digital pH pen; the color-drop kits are hard to read accurately. Calibrate the pen with buffer solution regularly or it drifts and lies to you. Test your nutrient solution after mixing in your feed, since nutrients change the pH. Then adjust with pH Up or pH Down in small amounts, stirring and retesting until you hit your target.
- Mix your nutrients into water first.
- Test the pH of the finished solution.
- Add a few drops of pH Up or Down, stir, and retest.
- Feed once you are in range for your medium.
- Test the runoff to see what the root zone is actually doing.
Pair pH management with a sensible feeding routine from our nutrients and feeding guide. Your medium matters too; see best soil for cannabis clones and soil vs coco vs hydro for how each behaves.
Reading runoff and spotting lockout
Testing the water that drains from your pot tells you the real root-zone pH, which can differ from what you poured in. If input pH is correct but runoff is off, your medium is shifting it, often from salt buildup. Flushing with pH-corrected water resets it. When leaves show deficiency signs but your feed is dialed in, suspect pH lockout before adding more nutrients. Our nutrient deficiency guide helps you tell the two apart.
Every technique here works better with strong genetics. Browse our rooted, HLVd-tested clones or start with forgiving beginner strains.
Frequently asked questions
What pH should cannabis water be?
Adjust your nutrient water to about 6.0 to 6.5 for soil and 5.5 to 6.0 for coco or hydroponics, testing after you mix in nutrients since they shift the reading. Feeding in the correct range keeps every nutrient available to the roots. Always correct pH just before you feed, not before adding nutrients.
What happens if pH is too high or too low?
Out-of-range pH causes nutrient lockout: specific nutrients become chemically unavailable, so the plant shows deficiencies even though the nutrients are present. High pH commonly locks out iron and manganese; low pH can lock out calcium and magnesium. The fix is correcting pH, not adding more nutrients, which often makes things worse.
Do I need to pH water in living soil?
Well-buffered living soils self-regulate pH and many growers water them without adjusting. Still, testing your input water and occasional runoff is smart, since very hard or alkaline tap water can push the root zone out of range over time. If your plants stay healthy, a hands-off approach is fine; if deficiencies appear, start testing.
How do I lower or raise pH?
Use commercial pH Down (usually phosphoric acid) to lower and pH Up (usually potassium hydroxide) to raise, adding a few drops at a time, stirring, and retesting until you hit your target. Make small adjustments; it is easy to overshoot. A calibrated digital pH pen is essential for accurate, repeatable results.
When pH drifts out of range it often triggers nutrient lockout, where the nutrients are present but the roots cannot take them up.
Dial in your pH and your genetics can reach their full potential. Browse our cannabis clones for sale and grow female-guaranteed, freshly rooted plants built to thrive.