Q. What's wrong with my 14 year old prayer plant? It's leaves are curling.
Your fourteen year old prayer plant, Maranta leuconeura, has lasted a very long time and I’m sure you want to keep your old friend happy and healthy. So during the winter rest period, water it sparingly, allowing the top half of the mixture to dry out between waterings. Temperature of 65 to 70 degrees F. is ideal. When the plant starts growing more in the coming warm, weather, you can water plentifully to keep it moist.
Indoors, especially during winter, extra humidity is in order since indoor, relative, humidity is extremely dry; a pebble tray would help make a micro-climate for your plant as an alternative to an electric humidifier. A pebble tray is made with an inch or more of small pebbles placed in a larger tray or saucer, then filled with water halfway up the pebbles. The water shouldn’t touch the bottom of the plant’s container, or roots may stay too wet and rot. A much larger pebble tray is best for more surface area of pebbles/water, but use a separate saucer under the pot and place it over the pebble tray.
If needed, you can move your plant into a new container one size larger in spring, but you may not have to do that if the roots fit the container. Marantas do not have a deep root system and grow well in half pots.
I think your plant may need more humidity and has possibly been kept too wet or too dry. Let me know if this helps.
Courtesy of the NYBG Plant Information Service