Why do Calathea leaves close?
Also question is, why do Calathea leaves curl?
The leaves of a Calathea Plant curl under when the temperature is too warm or the Calathea Plant is in an area that is too bright. Here are some things that might be causing the problem: water with too many chemicals or if it is too hard or too soft, over fertilization, direct sun, lack of humidity, and plant diseases.
In this manner, why is my Calathea not closing?
If it sits near a lamp or other light source at night, it may not be getting dark enough for the leaves to fold up. Try moving it to a new location away from the light to see if it adjusts to light and dark conditions.
A healthy calathea will slowly turn its leaves to catch ambient rays of sunshine; an unhealthy calathea will curl its leaves tightly to signify distress. Once you fix the problem, the leaves might even uncurl before your eyes. Move your plant out of the light.