pH by growing medium
| Medium | Ideal pH | Notes |
|---|---|---|
| Soil | 6.0 – 7.0 | Buffered and forgiving; sweet spot 6.3–6.8. Let it drift WITHIN range — different nutrients uptake at different points. |
| Coco / soilless | 5.5 – 6.5 | Behaves like hydro; needs cal-mag; target 5.8–6.2 in, watch runoff. |
| Hydro / DWC / rockwool | 5.5 – 6.5 | No buffer at all — small drifts matter fast; 5.8 is the classic anchor. |
Out-of-range pH locks out nutrients that are physically present — which is why it mimics deficiency (see the deficiency chart). Logging pH on every feed is the cheapest insurance in growing.
Common questions
What pH should I run in soil, coco and hydro?
Soil 6.3–6.8, coco 5.8–6.2, hydro 5.5–6.0. Soilless and hydroponic systems run lower because there is no soil buffer holding pH steady — the target is the solution itself, not a reservoir of exchange sites.
Why do nutrients lock out at the wrong pH?
Availability is chemical, not biological. Micronutrients in particular fall off sharply as pH rises — extension research describes zinc, copper and manganese dropping roughly a hundredfold per pH unit. The nutrient is still in the pot; the plant simply cannot take it up.
Is it lockout or an actual deficiency?
The leaf symptoms are identical, which is why guessing fails. Check runoff or solution pH first — if pH is in band and the symptom persists, treat it as a real deficiency; if pH has drifted, correct that before adding anything.
Does pH drift matter if the average is right?
Yes. A solution swinging 5.2 to 6.6 spends time outside the band for several nutrients even though the mean looks fine. Stability beats a good average.
Sources: Veazie et al. 2025 — substrate pH and micronutrient uptake in cannabis · Cockson et al. 2019, Applied Sciences — cannabis nutrient sufficiency ranges · Univ. of Maryland Extension FS-1054 — pH and nutrient availability · Oklahoma State Extension HLA-6722 — why hydro runs lower than soil
- Digital pH pen — a $20 pen prevents most nutrient problems outright
- pH up / pH down kit — adjust runoff and reservoir without guessing
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