Calathea and Maranta
Calatheas and prayer plants like consistently damp soil and are often sensitive to minerals in tap water. Leaves that curl are their way of asking for a change.
Your answer
Water when the soil reaches this point
How it shifts through the year
Curling usually means thirst or dry air. Check the soil, and move the plant away from heating vents if the air is dry.
Many owners get better results with filtered or rainwater, since these plants can be sensitive to minerals in hard tap water.
Tools that help
As an Amazon Associate I earn from qualifying purchases.
Related guides
Estimates use rules of thumb. Always confirm with your finger: push it about an inch into the soil before you water.