The most common cause of yellowing leaves among Pothos plants is improper soil moisture–in particular, overwatering. Only water your Pothos when the top 25% of the soil in the pot is dry. Soil should remain damp, but not wet or soggy. In the winter, you can allow your plant to dry out a little more between waterings, but be sure to boost the humidity around your plant with regular misting, a humidifier, or pebble tray.
When you water your Pothos, make sure you provide enough water so that liquid flows from the drainage hole at the bottom of the pot and into the saucer. It’s extremely important to discard any excess water in the saucer and not to let your plant sit in any standing water. Your Pothos will not respond well to “wet feet,” which will cause the roots to rot and lead to the eventual death of the plant.
Providing proper and consistent soil moisture is important in caring for a Pothos. Alternating between bone dry and wet soil from ill-timed waterings can create stress and cause the leaves of your Pothos to yellow.
Your humidity level
Low humidity and dry soil cause leaves to droop and brown on their edges, later followed by entire yellowing, browning, and leaf drop. Misting the leaves of your Pothos often will increase the humidity.
Pothos will grow best when placed in bright to medium indirect sunlight, but they will adapt to lower light if needed. However, if placed in very low light, yellow leaves may develop. Be careful you’re not placing your Pothos in full sun–when exposed to direct sunlight for too long, the foliage will burn.
A weakened or stressed Pothos is 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 frond parts into nooks and crannies. The piercing mouths of the insects exhaust your plant and accelerate yellowing, especially if your Pothos is already unhealthy from poor lighting, a nutrient deficiency or improper soil moisture.
Some yellowing is natural
Is your Pothos pushing out new growth? If there is new growth on your plant and the yellowing leaves are older, particularly at the bottom of the plant, this yellowing is natural. Your plant sheds its old leaves and sends energy to new growth.