What pH is
A scale from 0 to 14 that measures how acidic or alkaline something is. 7 is neutral; lower is acidic (lemon is 2), higher is alkaline (bleach, 12). Each point is 10 times more: a pH of 6 is ten times more acidic than a 7.
Why it matters
Each nutrient can only be absorbed within a pH range. In soil, cannabis takes everything up well between 6,0 and 7,0 (ideal 6,2 to 6,8); in coco or hydro, between 5,5 and 6,5. Outside that range, the nutrients are there but the root can't take them up: this is called lockout.
How you can tell
The plant shows deficiencies (yellow leaves, spots, broken tips) even though you are feeding it. The typical mistake is giving more fertilizer, which makes everything worse. Calcium, magnesium and iron are the first to get locked out.
Where it comes from
Fertilizers, on the other hand, usually lower it.
How to fix it
You measure the pH of the watering water (with the fertilizer already mixed in) and adjust it with a few drops of pH down (pH-) or pH up (pH+), little by little, mixing and measuring again. You can also measure the water draining out the bottom, which shows how the soil is doing.
▲ Pros
- With the right pH, every dose counts
▼ Cons
- Without a meter it's hard to notice
🎮 Practice it in UnderGrow
It's grown in soil: the root takes up nutrients well between 5,6 and 6,8. Tap water (pH 7,4) keeps pushing it up; rain is pH 6,5 and fertilizer lowers it a little. Watering with corrected pH brings it closer to pH 6,2 (halfway each time) and flushing with pH down leaves it at pH 6,2. Without a pH meter you don't see it until the plant turns yellow.
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