Home / Glossary / Nutrients Media
pH
Definition: pH is a 0 to 14 scale that measures how acidic or alkaline a solution or growing medium is, with 7 being neutral. For cannabis, pH controls which nutrients roots can actually absorb, so growers keep soil around 6.0 to 7.0 and soilless or hydroponic setups around 5.5 to 6.5.
How pH works
The scale is logarithmic: a pH of 5.0 is ten times more acidic than 6.0. Small number changes therefore mean big chemical shifts in the root zone.
Why it matters
Each nutrient dissolves and stays available within its own pH window. Iron and manganese become harder to absorb as pH climbs toward 7.5. Calcium and magnesium get scarce when soilless pH falls much below 5.5. When pH drifts outside the comfortable band, plants can show deficiencies even with plenty of fertilizer present, a problem known as nutrient lockout.
Targets by medium
| Medium | Target pH |
|---|---|
| Soil | 6.0 to 7.0, often aimed at 6.3 to 6.8 |
| Coco coir | 5.8 to 6.2 |
| Hydroponics | 5.5 to 6.2 |
In hydro and coco, letting pH drift gently within the range is fine, even helpful, because different nutrients peak at slightly different points.
Measuring and adjusting
- Use a digital pH pen and calibrate it with pH 7.0 and 4.0 buffer solutions every couple of weeks.
- Store the probe in storage solution, never distilled water, which shortens its life.
- Mix nutrients first, then test and adjust with pH up or pH down a few drops at a time.
- Check runoff pH occasionally to see what the root zone is really doing.
An exception
Well-built living soil buffers pH through its biology and organic matter, so many organic growers water without adjusting at all.