Cannabis Nutrient Deficiencies: Read the Leaf, Find the Cause
Most feeding panics start with one discolored leaf and a guess. They do not have to. A nutrient deficiency writes its cause onto the plant in a readable pattern — which leaves go first, where the yellowing sits, whether the edges or the veins are affected. Learn to read that pattern and you stop reacting to symptoms and start fixing causes.
The single most useful question: did the problem start on the old, lower leaves or the new, upper growth? That one split sorts most deficiencies before you touch the bottle.
Nitrogen deficiency, early to severe.
Nitrogen is mobile, so a short plant pulls it out of its oldest leaves to feed new growth. That is why nitrogen deficiency always starts at the bottom and climbs. Caught early it is a trivial fix; left alone it strips the lower canopy. Use the progression below to locate where your plant actually is — the correction depends on the stage, not just the color.
One caveat that saves a lot of overfeeding: a little fade late in flower is normal and even desirable as the plant uses up its reserves. Read nitrogen loss against the calendar — early veg, fix it; last two weeks, often leave it.
Where the symptom starts tells you what to suspect.
| What you see | Where it starts | Most likely cause |
|---|---|---|
| Even yellowing, whole leaf | Old, lower leaves | Nitrogen deficiency |
| Yellow between green veins | Old, lower-to-mid leaves | Magnesium deficiency |
| Brown spots and burnt edges | Mid leaves | Potassium or calcium |
| Yellow new growth, green veins | New, upper leaves | Iron (often pH lockout) |
| Many symptoms at once, fast | Anywhere | pH lockout, not a single nutrient |
If several symptoms appear together and spread quickly, stop adding nutrients. That pattern is almost always pH lockout — the nutrients are present but the root zone pH has drifted out of the range the plant can absorb. Fix the pH and the "deficiencies" resolve on their own. In hydro, that conversation starts at the reservoir; see root problems in DWC.
Cannabis nutrient deficiency questions
How do I tell a nutrient deficiency from nutrient burn?
Look at where it starts and what it does to the tips. Deficiencies usually fade or discolor whole leaves from the inside; nutrient burn browns and curls the very tips of healthy green leaves, often on the upper canopy where feeding is strongest. Burn means back off; deficiency usually means feed or fix pH.
Should I check pH before adding nutrients?
Almost always. Most apparent deficiencies are really pH lockout — the nutrient is in the reservoir or soil but cannot be absorbed at the current pH. Adding more nutrient to a locked-out plant makes things worse. Confirm pH is in range first, then decide if anything is actually missing.
Is some yellowing normal late in flower?
Yes. As harvest approaches, the plant draws down stored nitrogen and the lower leaves fade. A gentle fade in the final weeks is expected and is not a problem to chase. Aggressive yellowing early in the cycle is the version worth correcting.