Plants for humid air

Central heating is drier than almost any place a houseplant comes from. A living room in winter often sits at thirty per cent relative humidity, and the forest floor a calathea evolved on is nearer eighty. Most houseplants cope with the gap. The plants on this page do not, and they say so in brown crisp edges, in leaves that fail to unfurl properly, and in spider mites, which breed happily in dry warm air and hardly at all in damp.

Humidity is the hardest condition to change in a house, which is why the honest advice is to choose plants that suit your rooms first, and to keep the demanding ones in the one room that suits them.

What works, and what does not

Misting does not work, in the sense of raising humidity. Water sprayed on a leaf is gone within the hour, and the air around the plant is back to the room’s own dryness. It is not useless: it washes dust off, and it makes life slightly harder for spider mites. It is simply not the answer to a plant that needs damp air.

Grouping is free and does work. Plants transpire constantly, and a cluster of pots creates a pocket of air measurably more humid than the room. Six plants together do more for each other than any of them could do alone.

A pebble tray works if it is built properly. A wide, shallow tray of gravel with water filled to just below the top of the stones, and the pot standing on the stones rather than in the water. The evaporating surface has to be larger than the pot for it to be worth doing.

A humidifier works best of all, and it is the only method that will hold a room at fifty or sixty per cent through a winter. A small one running in the room where the plants are grouped is a better investment than a large one in a hallway.

Warmth and damp air belong together

Humid air and cold together bring rot and fungal spots, so the plants here want both: warmth in the low twenties and air that is not parched. A steamy bathroom that drops to fourteen degrees overnight is worse for a calathea than a dry warm living room is.

Water quality is worth a thought too. Several of the plants on this page, calatheas and marantas in particular, mark badly with the fluoride and chlorine in tap water. Rainwater, or tap water left to stand overnight, keeps the leaves cleaner.