Photo: sc-images, depositphotos
By Larry Hodgson
I’ve long been fascinated by bird’s-nest ferns (Asplenium nidus and similar species, such as A. antiquum and A. australasicum). They get their name because of their very unfernlike fronds—they’re simple and tongue-shaped rather than deeply cut like most fern fronds—and because they form an open, cuplike rosette much like a bird’s nest.
Also, to carry the bird analogy a step further, their young fronds, still pale green, are rolled up like a ball at first and can be said to look like eggs sitting in the hairy brown crown at the center of the nest, something you’d most likely see only in spring, just as the plant is starting to go into a growth spurt.
The fronds are shiny and mid-green with a prominent black midrib. The plant forms a thick “trunk” of dark brown rhizomes as it ages, although that may take years.
Likewise, sores (spore-bearing organs), which appear as narrow brown lines angling out from the midrib on the underside of the frond, are usually only produced on mature plants.
Obviously, there are no flowers, since ferns are “primitive plants” and never bloom.
A Way of Coping With a Harsh Aerial Lifestyle
As cute as this bird’s nest habit might seem to humans, it didn’t evolve that way to please our eye, but has a very practical purpose.
Bird’s-nest ferns are essentially epiphytes (plants that grow on tree trunks and branches), although they’re also found on rock faces and sometimes fall to the ground and continue growing as terrestrial plants. The epiphyte lifestyle is a difficult one: the bare bark their roots cling to offers little in the way of moisture and minerals, but bird’s-nest ferns’ special shape helps them compensate. Their “nest” catches and holds fallen leaves, bird droppings and other detritus which can then decompose slowly, feeding the fern. The detritus also holds moisture, helping the fern cope with dry spells.
Botanists call the plants with this growth habit “trash-basket plants,” a rather unfortunate name, don’t you think? Other names include litter-gathering plants, nest-epiphytes and detritophylic plants. I prefer to think of them all as bird’s-nest plants, a much more sympathetic description.
Curiously, sometimes birds actually do build nests in bird’s-nest ferns. The Madagascar serpent-eagle (Eutriochis astur), for example, often forgoes building a nest of its own and simply sets up shop in the ready-made nest of a large bird’s-nest fern.
Putting a Botanical Name on a Bird’s Nest Fern
There are over 30 species of bird’s nest ferns in the genus Asplenium, all with the same basic habit. They are native throughout the tropics and subtropics of Asia, Africa and Oceania.
What species is your bird’s nest fern? My suggestion is not to worry too much about the proper botanical name for any bird’s nest fern, as confusion reigns in their nomenclature. Even taxonomists confuse the various species. In fact, it is highly likely that even “well-known” species like A. nidus are actually composed of several as yet unidentified ones. That’s why some specialists use the term A. nidus senu lato for any fern of this type. It essentially means “A. nidus in a broad sense.”
If you do want to try and figure it out, the three following are the ones most currently offered:
A. nidus is the classical houseplant bird’s nest fern, grown since Victorian times. It has fairly broad fronds, quite thick, and often slightly wavy along the edges. It eventually grows to a large size. Fronds over 5 feet (1.5 m) are not unheard of outdoors in the tropics and in humid greenhouses, but don’t expect anything bigger than about 12 to 18 in (30 to 45 cm) under average home conditions.
A. australasicum is similar, but somewhat smaller, and thoroughly confused with A. nidus in the trade. It’s best told apart from its cousin by the fact that it has a prominent midrib under the frond and not just on top, giving the frond a wedge shape.
A. antiquum or Japanese bird’s nest fern is a much smaller plant than the other two and currently very popular through a few of its wavy-leaved cultivars. If yours has narrow, thin fronds with a pointed tip rather than a rounded one and a midrib that is green, it’s probably an A. antiquum.
As for the many cultivars, they all show fronds attractively mutated in one way or another. All of the following are variously attributed to A. nidus, A. antiquum or A. astralasicum depending on which expert you speak to:
Some, such as ‘Crissie’, have fronds that are forked at the tip. Others, like ‘Leslie’, are even more abundantly cut at the tip and are said to be crested.
Some have serrated fronds, that is, with cut edges, like ‘Fimbriatum’, although these don’t seem very popular these days.
Many cultivars have fronds with wavy margins. They can be lightly waved, as in ‘Victoria’ or abundantly undulated, like ‘Osaka’ and ‘Crispy Wave’.
The “plicata” type (often called lasagna fern), such as ‘Cobra’, has fronds that are folded like a fan on both sides, making them look like green lasagna! I find the plicata types harder to grow well than the others.
And then there is ‘Hurricane’, a recent introduction whose fronds not only have wavy edges, but twist into a bit of a spiral.
Caring for a Bird’s Nest Fern
You’ll often see bird’s nest ferns offered as being easy to grow, but I don’t agree, at least, not when they grow as houseplants. (Outdoors in the humid tropics, though, they are tough, no-nonsense garden plants!) My experience is that they “hold” very well and may look fine for several months, but then start to decline. They may still live for a few years, but soon come to disappoint. Of course, that’s if you give them standard care.
If you want a great bird’s nest fern, you just have to give it premium care.
Light: In the wild, these ferns grow in partial or deep shade, but indoor conditions are generally much darker than those outdoors. So, they’ll prefer intense to medium light indoors, perhaps near an east window. So, yes, they can easily take a few hours of sun per day, but do protect them from full sun in the heat of the summer. They are unlikely to truly thrive under low light, unless you can supply high humidity. (They best carry out photosynthesis when the air is steamy.)
Watering: Many people think ferns need even soil moisture and so water these plants too much. But remember, bird’s nest ferns are epiphytes, growing way up in trees where they’re exposed to drying air and thus their roots dry out from time to time. Water them according to the golden rule of watering: when the soil is dry to the touch, water thoroughly, but not before. That might be once a week or even less, especially during the winter. But they do have to dry out a bit; you can’t just keep them moist all the time.
And water only the soil. They are not tank bromeliads and you shouldn’t pour water into the “nest,” as that can cause staining and damage.
If your water is very hard, you might consider watering at least occasionally with rainwater, distilled water or humidifier water … or leaching from time to time.
Atmospheric Humidity: Lack of good air humidity is the main problem with growing bird’s nest ferns. They have a hard time adapting to the dry air found indoors, especially over the winter. Ideally, they’d need an atmospheric humidity of 70% or more; in other words, greenhouse conditions. At 50% humidity, they might do all right, but expect some damaged leaves (brown tips and irregular edges can be signs of dry air damage). A humidifier will likely be needed to keep them happy. Either that, or grow them in a bathroom or other room where the air is humid to the point of being stuffy.
I used to put mine in a sealed terrarium (an old aquarium with a glass top) over the winter and it loved it. As it got bigger and outgrew the container, I started growing it inside a clear plastic bag. That certainly did the trick! In fact, it started producing spores that clearly wafted through my home in moving air, as I used to find baby bird’s nest ferns sprouting in all my seed trays in the basement although the mother plant was upstairs!
Fertilizer: This plant receives few minerals in the wild, growing as it does way up on a tree trunk far from any soil, and is not terribly tolerant of soil minerals. The potting mix you use likely contains all the minerals it could ever use. If you do fertilize, use only a very dilute dose and only during the spring to summer growing season. Be especially careful not to use fertilizers extra rich in nitrogen.
Overfertilized fronds take on irregular shapes and yellow or brown colorations.
Temperature: These ferns are from the tropics and don’t like cool temperatures. They can tolerate down to 50 ˚F (10 ˚C) for short periods, but temperatures in the 60 to 80 ˚F (16 to 27 ˚C) range are much more suitable.
Grooming: Cut off older fronds as they turn yellow then brown. And any other damaged fronds as needed.
Repotting: This plant fills its pot with very fine brown fibrous roots. They actually cling to the pot sides and you may need to run a knife around the inside of the pot to free the plant.
In a sense, the plant only actually needs repotting when it becomes top-heavy and no longer stands up on its own, as it can grow for decades in the smallest of pots. However, it is sensitive to mineral salt buildup, so repotting into fresh soil ever two or three years is wise.
The thick “trunk” that begins to form over the years is not all that attractive. If you don’t care to watch it develop, when you repot, cut off a slice of root ball equal in height to the trunk and lower the plant into its new pot. When you can then add soil around the trunk, burying it … which it will soon produce roots into the freshly added soil.
Any commercial potting mix will do for repotting, even orchid mix.
Special Care: A summer outdoors in the shade will allow warm rains to help leach the potting mix of excess mineral salts, so is particularly beneficial to this plant.
Multiplication: Few home gardeners multiply their bird’s nest ferns, but rather buy new ones. Today’s cultivars are test tube babies, grown in in vitro culture from only a few meristem cells. You can also multiply them by spores … except they rarely produce any under average home conditions, plus they aren’t all that available commercially either. If you do come across some, here are some details on how to sow them: Grow Your Own Ferns from Spores.
Sometimes, too, you may buy a pot with more than one fern in it, in which case you could simply separate the plants and pot them up individually.
Theoretically, you divide a single plant as you would a pie, chopping its crown into wedges and potting up each wedge under high humidity (under a clear plastic dome or inside a transparent plastic bag), as this is quite a shock for the plant. As it sets the mother plant back several years, few people want to risk it. Sprouts may take months to appear.
Toxicity: This is plant is considered safe for humans and pets. It is, in fact, grown as a vegetable in Asia for its edible fronds.
Problems: Dry air, mineralized soil and constant drought cause brown and deformed fronds. Rot can be a problem in heavy, wet soils or pots with no drainage. Bird’s nest ferns can be affected by common houseplant insects, such as scale, mealybugs and aphids, but this tends to be quite rare.
The bird’s nest fern: you may never know exactly what species it is, but it certainly creates an attractive effect in the living room, kitchen or office!