Yellow leaves on cannabis most often mean a nutrient shortage, a pH lockout, or a water problem. Leaf position gives the first clue. Lower leaves that turn yellow point to nitrogen or magnesium. New leaves that yellow point to iron or sulfur. Yellowing late in flower can be normal senescence, not a deficiency.
Cannabis Yellow Leaf Treatment: Causes and Fixes
Identify which leaves are yellow
Look at the whole plant before you add anything. Note whether the color loss starts at the bottom, the top, or the edges, and whether the veins stay green.
Why Are My Cannabis Leaves Yellow?
- Lower leaves, uniform pale yellow: nitrogen deficiency.
- Lower leaves, yellow between green veins: magnesium deficiency.
- New leaves, yellow with green veins: iron deficiency.
- Leaf edges yellow or brown: potassium deficiency or salt buildup.
- Top leaves bleached or yellow under a strong light: light stress.
Check water and drainage
Overwatering and poor drainage cause lower-leaf yellowing that looks like a nutrient problem. Roots need oxygen, and soggy media starves them.
- Lift the pot and compare its weight with a dry pot of the same size.
- Press a finger 2 inches into the media. Water only when the top layer is dry.
- Confirm the pot has open drainage holes and empty the saucer after watering.
- Stop watering for several days if the media stays wet and the leaves droop.
Measure pH and runoff
Nutrients can be present in the media and still unavailable when pH is outside the usable range. Test before you add more fertilizer.
why are my cannabis leaves yellow
- Measure the pH of the water or nutrient solution before watering.
- Water until runoff exits the pot and catch the runoff in a clean cup.
- Measure runoff pH and compare it with the input pH.
- Adjust in small steps: keep soil near pH 6.0 to 7.0 and coco or hydro near pH 5.5 to 6.5.
Match the fix to the cause
- Nitrogen: feed a balanced vegetative nutrient at the label rate.
- Magnesium: add a magnesium source such as Epsom salt at a low rate, then watch new growth.
- Iron: correct pH first; iron is unavailable in alkaline media.
- Overwatering: improve drainage and let the media dry between waterings.
- Light stress: raise the fixture or reduce intensity, then check the top canopy after 3 days.
Know when yellowing is normal
In late flower, cannabis pulls mobile nutrients from older fan leaves. A few lower leaves yellow and drop while buds swell. That process is senescence. Do not treat it with a heavy nitrogen feed, which can delay finishing and leave harsh material.
Change one variable at a time
Apply one fix, wait 3 to 5 days, and check the same leaves. Do not add multiple nutrients, change pH, and repot in the same week. Damaged leaves will not turn green again. Judge the fix by new growth and by whether yellowing spreads.