Why are my Calathea leaves curling?

First, rule out normal nighttime curling

Calatheas are prayer plants, and curling is part of their daily rhythm. Each evening they fold and raise their leaves, then open them again by morning. This movement is called nyctinasty, and it is a sign of a healthy, responsive plant, not a problem. Before you change anything, watch the plant through a full day. If the leaves relax and flatten in the morning light, nothing is wrong. You only have something to fix when leaves stay curled or tightly rolled during the daytime.

The thirst test: soil dryness vs. dry air

Daytime curling on a Calathea comes down to water, and there are two separate sources of thirst. The plant can be dry at the roots, or it can be losing moisture to dry room air faster than it can replace it. Both make the leaf roll inward, so you need to check each one.

Press a finger into the soil up to the first knuckle. If the top inch is dry, the pot feels light, and the edges are crisping, the roots are thirsty: water it. If the soil is still lightly moist but the leaves curl anyway, especially in winter or near a heater, the culprit is dry air. Calatheas come from humid tropical forest floors and want 50 to 60 percent humidity or higher. Once room humidity drops below about 40 percent, edges curl and brown even when the soil is fine. A cheap hygrometer settles the question in seconds.

A quick worked example

Say only your newest, innermost leaves are tightly curled while the older outer leaves still look flat and healthy. That pattern points to underwatering or low humidity, because new growth is the first to suffer when water is scarce. Now compare that to a plant where the leaves facing a bright window are curling, fading, or developing pale scorched patches while the shaded leaves stay fine. That pattern points to too much light, not thirst. The location of the curl tells you which problem you have before you change a thing.

Other causes worth checking

If the soil is moist, humidity sits above 50 percent, and the light is gentle, work down this ranked list.

• Too much light or heat: Curling with faded or scorched patches on the leaves nearest the window. Calatheas want bright indirect light, the kind you get a few feet back from an east window or behind a sheer curtain on a south or west one. Direct midday sun bleaches and curls the leaves.
• Hard or treated tap water: Brown, crispy edges and curling that builds slowly over weeks. Calatheas are unusually sensitive to the fluoride, chlorine, and dissolved salts in hard tap water, and the damage shows up as marginal browning before the leaf rolls.
• Cold or drafts: Calatheas dislike temperatures below about 60 F (16 C) and react to cold windowsills, air-conditioning vents, and door drafts with curling and limp leaves.
• Spider mites: Curling with fine webbing and tiny pale speckles. Check the leaf undersides with a magnifier for slow-moving dots, since dry indoor air invites them.

How to fix curling Calathea leaves

1. Water thoroughly until it drains from the bottom, then let only the top inch dry before watering again, usually every 5 to 7 days.
2. Raise humidity to 50 to 60 percent with a humidifier, a pebble tray, or by grouping plants together.
3. Move the plant to bright indirect light, away from direct sun, heaters, and cold drafts, and keep it above 60 F (16 C).
4. Switch to distilled water, rainwater, or tap water left out overnight so the chlorine can off-gas.
5. Inspect leaf undersides for spider mites and rinse or treat with insecticidal soap if you find them.
6. Trim fully crisped tips and wait for healthy new growth, which is the real sign of recovery.

Does the cultivar matter?

The diagnosis is the same across the popular Calatheas, but some show stress sooner. Thin-leaved types like orbifolia and white fusion are the quickest to curl and crisp in dry air, and white fusion in particular sulks at the slightest neglect. Medallion and rattlesnake (lancifolia) are a little more forgiving but still want humidity and soft water. Whichever you grow, treat steady moisture, soft water, and humid air as the baseline rather than a rescue.