Quick Tip: Water until water comes out of drainage holes. Allow top 2 inches of soil to completely dry between waterings.
Philodendron selloum plants appreciate a consistent, but not overly wet, level of moisture. The ideal time to water them is when the top inch of soil is completely dry, after which you should water well, letting any extra water drain out of the bottom of the pot. It's crucial not to allow the plant to stand in water that is still because this can cause root rot. Also, keep water off of the plant's leaves to prevent the spread of illness and fungus. Throughout the winter, when development slows, water the plant less frequently, and avoid placing it in a drafty area where the soil can dry up too rapidly.