Why is my Calathea undulata plant drying out?

This is a great opportunity to learn about soil mixtures! To create a soil mixture that has good drainage, you can use peat moss, orchid bark, perlite, and coco coir. The ratio is 2 parts peat moss and coco coir, 1 part perlite and orchid bark. Have fun experimenting with different ratios to see what works best for your plants!