Cannabis Leaves Yellowing From Bottom Up? Causes & Fixes

Yellowing cannabis leaves that start at the bottom and creep upward almost always point to a mobile nutrient deficiency, with nitrogen as the top suspect. Mobile nutrients get pulled from older, lower leaves to feed new growth up top, so the bottom fans fade first. The color pattern tells you which nutrient is missing: uniform pale yellow means nitrogen, yellow between green veins means magnesium, and yellow edges that turn brown and crispy mean potassium.

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Why do cannabis leaves yellow from the bottom up?

Nitrogen, phosphorus, potassium, and magnesium are mobile inside the plant. When supply runs short, the plant robs older leaves and sends those nutrients to the growing tips.

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That is why new growth stays green while lower leaves turn yellow. Immobile nutrient problems, such as calcium or iron deficiency, do the opposite and show up on new leaves first.

cannabis yellow leaves nitrogen deficiency

Which deficiency is it? Match the pattern

Nitrogen deficiency

Lower leaves turn a uniform pale yellow, then drop off as the fade climbs one node at a time. This shows up in veg, in heavy feeders, and after a long stretch with no feed.

Magnesium deficiency

Yellowing appears between the veins while the veins stay green, usually on lower and middle leaves. Edges may curl up and tips can turn bronze. Common in coco, in soft water, and under strong LED lights.

Potassium deficiency

Leaf edges yellow first, then turn brown, dry, and crispy. The problem starts low and moves up. It shows up in late flower and in plants fed too much calcium or magnesium.

Normal late-flower fade

In the last two to three weeks of flower, plants stop taking nitrogen and lower leaves fade on purpose. If buds are swelling and only older fans yellow, the plant is finishing, not starving.

What else causes bottom-up yellowing?

• pH out of range, which locks out nutrients even when you feed correctly
• Overwatering and poor drainage, which suffocate roots
• Salt buildup in the medium after weeks of feeding
• Cold root zone below 65°F, which slows uptake
• Root rot or fungus gnat larvae chewing on roots

How do you fix yellowing leaves from the bottom up?

1. Check pH first. Aim for 6.0 to 7.0 in soil and 5.5 to 6.5 in coco or hydro.
2. Test runoff EC or PPM to see if salts have piled up in the pot.
3. Feed a balanced nitrogen dose if the pattern says nitrogen and you are still in veg.
4. Add a calcium and magnesium supplement if veins stay green between yellow patches.
5. Flush the medium with pH-correct water if runoff numbers come back high.
6. Let the pot dry back between waterings and keep root temps near 68 to 75°F.

Can yellow leaves turn green again?

Leaves that are fully yellow will not recover their color. New growth should come in green within a week of correcting the cause, and the yellowing should stop spreading upward.

Remove dead, crispy leaves so they do not invite mold. Watch the next two or three nodes to confirm the fix worked.

When should you worry?

Act when yellowing jumps two or more nodes in a few days, when leaves curl or spot, or when bud growth stalls. A steady, slow fade in late flower is normal.

Yellowing that starts low along with mushy stems, a sour smell, or wilting points to root rot rather than a nutrient shortage.