Zz plant leaves turning yellow?

Yellow leaves on a ZZ plant most often mean the roots have stayed too wet, though one old lower leaf yellowing slowly can be normal.

Answer what you can see

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Push a finger two inches into the soil. What does it feel like?

Which leaves are affected?

Where does it live?

How fast did this happen?

Some cases cannot be told apart by leaf color alone: overwatering or root rot and pests can both fit damp soil with yellowing all over after a week or two; direct sun and spider mites can both show yellowing on the window side; normal old leaf turnover and drought can both start on the oldest lower leaves.

The causes in full

Overwatering or root rotMOST COMMON

How to tell
The mix feels damp, soggy, or heavy for days, and if you slide the plant out, unhealthy roots look brown or black, soft, or mushy instead of firm.

What to do
If the mix is not dry all the way through, do not water; let it dry, empty any saucer, and make sure the pot has drainage holes. If roots are mushy, cut off the rotten parts and repot into a fresh, fast-draining mix, then water only when the mix is dry all the way through.

Too dry for too longCOMMON

How to tell
The pot feels very light, the soil has shrunk from the pot edge, and yellowing starts after a long dry spell rather than while the mix is wet.

What to do
If the mix is dry all the way through, water thoroughly until water runs from the drainage holes, then empty the saucer. If water runs straight down the sides of a shrunken, bone-dry root ball, soak the pot for 20 minutes only because the mix is dry all the way through, then let it drain fully.

Direct sun or window heatCOMMON

How to tell
The yellowing is strongest on the side facing the glass, often with pale, tan, or scorched patches where sun hits the leaves.

What to do
Move the plant out of direct sun through glass and into bright but indirect light. Water only if the mix is dry all the way through; do not add water just because the leaves are yellow.

Too little light and slow dryingLESS COMMON

How to tell
The plant is in a dim spot, the mix stays damp for a long time, and yellowing creeps in slowly without clear sunburn marks or pests.

What to do
Move it closer to a window with bright but indirect light. If the mix is not dry all the way through, wait to water; once it dries, water only when the mix is dry all the way through.

Normal old leaf turnoverLESS COMMON

How to tell
Only one or two of the oldest, lowest leaves yellow slowly while the rest of the plant stays firm and green.

What to do
If it is only the oldest, lowest leaf or two over months, trim off the yellow leaf when it is mostly yellow. Do not water unless the mix is dry all the way through.

Scale, mealybugs, or spider mitesRARE

How to tell
Look closely along stems, leaf joints, and leaf undersides for sticky residue, brown bumps, white cottony bits, fine webbing, or tiny speckled yellow dots.

What to do
If you find pests, isolate the plant, wipe them off with a damp cloth or cotton swab, and use a labeled insecticidal soap or horticultural oil, not dish soap, repeating as directed. Keep watering separate from pest treatment: water only when the mix is dry all the way through.

Will it recover?

Yellow ZZ leaves will not turn green again; the goal is to stop the cause and get firm new growth.

Stopping it happening again

Grow ZZ plants in a pot with drainage, keep them in bright indirect light or a few feet from a window, avoid cold draughts and hot direct sun through glass, and water only when the mix is dry all the way through.