Calathea

The calathea grows on the floor of Brazilian rainforest, in permanent shade, in air that never really dries and in soil kept damp by a canopy that holds the rain. Every one of its reputed difficulties comes from being asked to live somewhere unlike that. It is not a fragile plant so much as a specific one, and if you can give it steady warmth, real humidity and water without chlorine in it, the round silver banded leaves are among the most striking things you can grow indoors. It was moved from Calathea into Goeppertia in 2012, and almost every label still says Calathea.

Light

Medium indirect light, and never direct sun. This is a plant that evolved under a closed canopy, and an hour of afternoon sun through glass bleaches the silver banding to a flat pale green that does not recover. A north window in the northern hemisphere or a south one in the southern suits it, or several metres back from a brighter window.

If in doubt, err dark. A calathea in a dim corner grows slowly and keeps its markings; one on a sunny windowsill fades within a fortnight.

Water and humidity

Keep the compost lightly moist, watering roughly every five days in summer and every nine in winter, always checking with a finger rather than trusting the interval. Let the surface dry slightly between waterings but never let the pot dry out, and never leave it standing in water.

Water quality matters more here than for almost any other houseplant. Chlorine, fluoride and dissolved minerals accumulate at the leaf edges and burn them brown, and no amount of humidity will stop it. Rainwater, or filtered water, or tap water left standing overnight in an open jug, makes a visible difference on new growth within a season.

Humidity is the other half. A bathroom or kitchen suits it, and elsewhere a tray of wet pebbles, a group of other plants and a position well away from radiators all help. The leaves curl inwards when the air is too dry, which is a useful early warning before the edges brown.

Feeding and repotting

Feed at a quarter to a half of the recommended strength, monthly through spring and summer, and not at all in winter. Overfeeding shows up as brown edges within a fortnight and is easily mistaken for a water problem.

Repot in spring, one size up only, into a peat-free compost with coir and a little perlite. A pot much larger than the root ball holds wet compost the plant cannot use, which brings on the yellow lower leaves that look like overwatering because that is exactly what they are.

Pruning and propagation

Cut damaged leaves out at the base of their stalk rather than trimming them halfway. Where you are tidying a brown edge, cut following the natural shape of the leaf and it stays inconspicuous.

Division at repotting is the only practical way to make more. Tip the plant out in spring, work the clump apart into pieces that each keep several leaves and a fair share of roots, pot them separately, and keep them warm, humid and shaded for a fortnight while they settle.

The nightly movement

The leaves rise in the evening and lower again in the morning, driven by a swollen hinge of tissue at the base of each stalk that changes shape with the light. It is where the family name of prayer plants comes from, and it is worth watching for as a health check as much as a curiosity: a plant that has stopped moving its leaves is usually too cold, too dry or too wet.

Ailments

Brown edges are water quality, dry air or feed, in that order. Curling leaves are thirst. Yellow lower leaves with a wet pot are drowning. Bleached banding is too much light. Spider mites arrive when the air is dry and are the pest to watch for. The ledger below has the fixes.