Yellow leaves on a ZZ plant almost always mean overwatering. Zamioculcas zamiifolia stores water in thick underground rhizomes, so it is built to cope with drought and quickly resents wet compost. If several leaves are yellowing at once and the soil is damp, cut back on watering. That is the fix in the large majority of cases.
Underwatering, low light and natural leaf-shedding can also turn ZZ leaves yellow, but they are far less common. Here is how to work out which one you are dealing with.
Overwatering
The ZZ plant is close to unkillable, but the one way to kill it is to water it too often. Its rhizomes rot when compost stays wet, and rot shows up as yellowing leaves, a mushy stem base, and sometimes a sour smell from the soil.
Check the compost first. If it is still damp several days after watering and leaves are yellowing, you are watering too often. Let it dry out fully, then water only when the top half of the pot is dry, which can be every 2 to 3 weeks. If the base feels soft, tip the plant out and inspect the rhizomes. Firm and plump is healthy; brown, soft and smelly is rot. Trim the damage, repot into dry, free-draining compost, and hold off watering for a week. Our guide to preventing root rot is worth a read here.
Underwatering
A ZZ left completely dry for months will eventually yellow too, usually starting with the oldest, lowest leaves and often with some leaf drop. The difference is the compost will be bone dry and the pot very light. If that is the case, give it a thorough water, let it drain, and return to a normal cycle. ZZ plants tolerate neglect far better than fussing, so when in doubt, underwater rather than over.
Light, Age and Other Causes
ZZ plants happily cope with low light, but very deep shade slows them and can cause occasional yellowing. Move the plant somewhere with brighter indirect light if it sits in a dark corner. Avoid strong direct sun, which scorches the leaves.
A single yellow leaf now and then, particularly an old one at the base, is just natural ageing. The plant sheds older foliage as it puts energy into new growth. There is nothing to fix; remove the spent leaf and carry on. For the wider picture across all plants, see why houseplant leaves turn yellow.
How to Fix a Yellowing ZZ Plant
- Feel the compost. Damp plus yellowing means stop watering and let it dry fully.
- Bone dry plus yellowing means give it a proper drink.
- Check the rhizomes and stem base for softness if you suspect rot, and repot if needed.
- Move it out of deep shade and away from direct sun.
- Going forward, water only when the top half of the pot is dry. Underwatering is far safer than overwatering with this plant.