The most common cause of yellowing leaves among Stromanthe plants is improper soil moisture–in particular, overwatering. Your Stromanthe likes to be kept damp (but not wet or saturated!), so keeping a regular watering schedule is key.
When you water your Stromanthe, 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 Stromanthe will not respond well to “wet feet,” which will cause the roots to rot and lead to the eventual death of the plant. Yellow and browning leaves are the first sign that root rot may be occurring.
Providing proper and consistent soil moisture is important in caring for a Stromanthe plant. Alternating between bone dry and wet soil from ill-timed waterings can create stress and cause your plant to yellow. This is not a drought-tolerant plant.
Your tap water could also be causing your Stromanthe’s leaves to yellow. Stromanthe plants are sensitive to the chemicals found in most tap water. Use filtered water or allow your tap water to sit out uncovered overnight before watering so chemicals such as chlorine and fluoride can evaporate.
Your humidity level
Low humidity and dry soil cause leaves to droop and brown on their edges, later followed by entire yellowing, browning, and shriveling. Your Stromanthe will appreciate a boost in humidity from regular misting, a humidifier, or pebble tray.
A weakened or stressed Stromanthe 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 Stromanthe is already unhealthy from poor lighting, a nutrient deficiency or improper soil moisture. Learn how to treat common houseplant pests here.
Some yellowing is natural
Is your Stromanthe 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.