Improper Light
A ZZ Plant thrives in low to medium light. When exposed to direct sunlight for too long, the leaves will yellow and burn. The ZZ Plant can adapt to very low light areas, so don’t be afraid to place it in a dark corner–that might be just what it’s craving.
Moisture
Providing proper soil moisture (or lack of moisture) is important in caring for a ZZ Plant. The number one cause of yellowing leaves among ZZ Plants is overwatering. ZZ Plants basically thrive off of neglect–they don’t need much water to survive. Only water when 100% of the soil volume is dry. Water until water flows freely from the drainage hole at the bottom of the pot. Be sure to discard any excess water that flows into the saucer. Your ZZ Plant doesn’t like “wet feet,” as this can lead to root rot and eventual death of your ZZ.
Your watering consistency
Alternating between bone dry and wet soil from ill-timed waterings can create stress and cause your ZZ to have yellow leaves.
Pests
Weakened or stressed ZZ Plants become more susceptible to insect infestations. Sap-sucking bugs like spider mites can drain your plant of moisture. This problem quickly manifests itself by yellowing leaflets and fronds. Scale, mealybugs, and spider mites occur frequently in indoor conditions. If not killed early on, these small pests proliferate and move all along leaves and fronds and into nooks and crannies. The piercing mouths of the insects exhaust your plant and accelerate yellowing, especially if your ZZ is already unhealthy from a nutrient deficiency or improper soil moisture.
