Why does my calathea have brown crisp edges on the leaves?

On a calathea this shows as a thin, even band of tan to brown, dry and brittle, along the edge of the round leaves, sometimes starting at the tip. The middle of the leaf with its silver banding stays green and the plant otherwise looks healthy.

Two causes lead for this plant, and they often work together: the air and the water. The Royal Horticultural Society says brown leaf tips and edges are usually a result of low humidity, and the NC State plant toolbox says brown edges and tips come from low humidity or from tap water that contains fluoride. The entry puts water quality first, then dry air, then feed. The plant grows in forest air that never dries, and it is watered about every 5 days in the growing season and 9 in winter, so a lot of tap water passes through the pot.

To tell them apart in a minute, think about when it began. Browning that started when the heating came on, that is worse near a radiator, and that eases in a bathroom, is the air. Browning that appeared steadily whatever the season, on a plant standing in a damp room, while other plants nearby are unmarked, is the water. Look at the surface of the compost and the drainage hole for a pale crust: that is the third cause, salts from feeding and tap water.

The third thing to rule out is the compost drying out completely. A pot that dried right through, with the compost shrunk from the side, browns the edges after a fortnight away. And the entry says that a strong feed shows as brown edges within a fortnight, so a plant fed above the quarter to half strength it asks for is the suspect.

Brown edges never turn green again, so judge the recovery by the new leaves. The entry says that rainwater, filtered water or tap water that has stood overnight makes a visible difference on new growth within a season. A new leaf takes a few weeks to open in the growing season, and in winter it takes longer.

What this plant wants

The fix

Switch to rainwater, raise the humidity around the plant, and halve the feed. Trim the brown off with scissors following the leaf shape.

Read on

Brown crisp edges on the leaves

The same sign on any plant, with the causes in the order they are likely.

Calathea care

Light, water, feeding, repotting and the rest of the entry.

Check it in the diagnoser

Opens with the plant, the part and the sign already chosen.