How to Increase Humidity for Indoor Ferns

Ferns are some of the most rewarding houseplants you can grow in a British home, and also some of the quickest to sulk. Give them the soft, damp air of a shaded woodland floor and they will reward you with fresh croziers unfurling week after week. Give them the dry blast of a centrally heated sitting room and you will find brown, brittle fronds that crumble at the slightest touch. The good news is that fixing the problem does not mean turning your living room into a rainforest. A handful of small, steady habits will do far more than any single dramatic gesture.

Why ferns struggle with dry indoor air

Most ferns evolved in damp, still, sheltered places, and their fronds are thin and finely divided with a large surface area. Unlike thick-leaved plants such as rubber plants or succulents, they have very little waxy protection to slow down water loss, so they transpire freely. When the air around them drops below roughly 40 per cent relative humidity, moisture leaves the fronds faster than the roots can replace it. The tips and edges crisp first, because they are furthest from the water supply.

In a heated British home, humidity of 30 per cent or even lower is common from October through to April, particularly in rooms with radiators running. Warm air also holds more moisture, which means dry air plus warmth is a double blow. Aim for 50 to 60 per cent relative humidity around your ferns, and you will see new growth that stays green all the way to the tip.

Group your ferns together

The easiest and cheapest trick is simply to cluster your plants. Every leaf in a group is transpiring, and the moisture they release creates a shared pocket of humid air around the foliage. A gathering of five or six plants in one corner can lift local humidity noticeably, often by 10 per cent or more.

• Move ferns together rather than scattering them through the house.
• Add other moisture-loving plants to the group, such as peace lilies, calatheas, spider plants or prayer plants.
• Keep the cluster away from radiators, draughty doorways and any spot where a fan or air conditioning unit blows directly over the leaves.
• Use a tiered shelf or staging so plants sit at different heights, which traps humid air more effectively than a single row on a windowsill.

Pebble trays: the simplest reliable method

A pebble tray is unglamorous, cheap and quietly effective. It works because water evaporates continuously around the pot without ever soaking the compost.

• Choose a shallow, waterproof tray, wider than the pot so there is plenty of exposed surface.
• Spread a layer of pebbles or gravel about two to three centimetres deep.
• Pour in water until it sits just below the top of the stones. The base of the pot must rest on the pebbles, never in the water, or the roots will rot.
• Top up every few days and give the tray a scrub once a month to keep algae and slime at bay.

One large tray holding several ferns is more effective than several small ones, and it saves a great deal of fiddling at the kitchen sink.

Mist carefully, not constantly

Misting is the technique everyone reaches for first, and the one most often done badly. A fine cloud of water does raise humidity momentarily, but in a warm room it evaporates within minutes, so it is a top-up rather than a cure.

• Mist in the morning, so foliage dries before the cooler evening. Damp fronds overnight in a cool room invite fungal problems such as botrytis.
• Use tepid water. Cold water shocks the leaves, and hard tap water leaves chalky white spots that are almost impossible to remove.
• Rainwater, filtered water or cooled boiled water is far kinder, especially in hard water areas.
• Spray the air around the plant and aim under the fronds as well as over the top, rather than drenching the leaves directly.
• Skip misting altogether on fuzzy or hairy-leaved ferns, which dislike sitting wet.

Make use of bathrooms and kitchens

Rooms where water is regularly used naturally hold more moisture, so a bathroom with a window is a superb fern home. A Boston fern or maidenhair on a shelf away from the direct line of the shower will thrive in the steam. Kitchens work well too, provided the plant is not sitting over a hob or beside an oven. Aim for bright, indirect light, such as an east or north-facing window, and keep the plant out of full midday sun, which will scorch the fronds whatever the humidity.

Longer-lasting solutions

If you have several ferns or a particularly fussy specimen, it is worth investing a little more effort.

• Double potting. Sit the pot inside a slightly larger waterproof container and pack damp sphagnum moss between the two. Keep the moss moist and it will release humidity steadily around the crown.
• A small humidifier. A modest electric unit with a built-in hygrometer, set to around 55 per cent, solves the problem for a whole shelf of plants. Clean it regularly.
• Glass cover. Small ferns such as maidenhair adore a terrarium, a glass cloche or even a large jar with the lid ajar. The enclosed air stays humid with almost no effort.
• Water thoughtfully. Use tepid rainwater where you can, water when the top of the compost is just starting to dry, and never let a fern sit in a soggy saucer.

Layer two or three of these methods together and you will notice the difference within a few weeks: fewer brown tips, glossier fronds and those lovely new croziers unfurling all through the darker months. Ferns are forgiving once their air is right, and a calm, green, faintly woodland corner is a genuinely soothing thing to have in a British home.