Bird’s nest fern

Identification and origin

Asplenium nidus belongs to the spleenwort family, Aspleniaceae, which has more than 700 species worldwide. It is native to the rainforests of island Southeast Asia (Borneo, Sumatra, Java, Sulawesi, the Philippines, the Moluccas, the Malay Peninsula), New Guinea, the Solomon and Caroline Islands, and Queensland in northeastern Australia. There it usually grows as an epiphyte, perched on trunks and branches without harming the tree that carries it.

It looks little like most people’s idea of a fern. The fronds are undivided and strap-shaped, glossy light green, often wavy along the edges, with a prominent brown-black midrib. They rise from a tight center where new fronds unroll, forming a funnel that suggests a bird’s nest. The rosette traps leaves falling from the canopy, which break down into compost that feeds the plant.

Like every true fern, it never flowers. It reproduces by spores, borne in sori lined up as thin brown lines on the underside of the fronds, in a herringbone pattern running from the midrib toward the margin.

In the wild, fronds can exceed 4 ft long and 8 in wide. In a pot they are usually 18 in – 2 ft long, and the plant reaches 18 in – 4 ft tall. Growth is slow.

Cultivar names are unstable, and the same name can be applied to quite different plants. There are very wavy forms such as ‘Crispy Wave’ and ‘Victoria’, crested forms with forked tips, and dwarf forms. The related species Asplenium antiquum, which is smaller, is also widely sold as a houseplant under the same common name.

Light

Give it bright, indirect light near an east- or north-facing window. Direct sun is its main enemy: it turns the fronds yellow and stops growth. Outdoors in the tropics it grows in shade or part shade under a tree canopy.

Watering

Water when the top 1 in of the mix feels dry, and never let the root ball dry out completely: this fern has no tolerance for drought. Pour water around the edge of the pot rather than into the heart of the rosette, and avoid wetting the fronds. Let the pot drain and never leave it standing in a full saucer, which rots the roots.

In spring and summer the plant grows and drinks more; in winter the mix stays moist longer. Feel the soil before each watering rather than following a fixed routine.

Air humidity matters as much as watering. During the heating season, set the pot on a tray of wet pebbles, keeping the base above the water, or run a humidifier nearby.

Potting mix

It needs a mix rich in organic matter, porous, moist yet well drained, with a rather acidic pH. A fern or tropical-plant potting mix works; when repotting, equal parts houseplant potting mix and peat moss or leaf mold gives good results. As an epiphyte, it can also grow with very little medium, mounted on a fiber slab.

From late spring through summer, feed once a month with a houseplant fertilizer at half the label rate. Ferns scorch easily when overfed. Do not fertilize in winter, nor for six months after repotting or bringing a new plant home.

Temperature

It grows best at 61–70 °F; somewhat cooler conditions, down to about 55 °F, are still acceptable, and nights a little cooler than days suit it. It cannot take frost and does not survive below 39 °F. Keep it away from radiators, fireplaces, heating vents and air currents.

Once frost is over it can spend the warm season outdoors in shade, but bring it in before night temperatures fall below 50 °F. In the ground it is grown in USDA zones 11a to 12b; in zone 9 it needs freeze protection.

Repotting

Because it grows slowly, repotting every two or three years is enough, in spring, when new fronds appear and roots fill the pot. Choose a container only slightly larger, keep the plant at the same depth without burying the crown, and handle it gently: the fronds are fragile.

Pruning

No pruning is needed. Remove old yellow or brown fronds at the base, never touching the center of the rosette, where all new growth starts. Keep the plant out of busy passageways so the foliage is not bruised.

Propagation

A single rosette cannot be divided: propagation is by spores, or by tissue culture in commercial production. Sowing spores takes patience but can be done at home.

Cut a frond whose sori have turned dark brown and lay it on white paper in a dry room with no air currents. After a few days a fine dust collects: these are the spores. Prepare a clear plastic box with a lid, washed and then soaked for ten minutes in a 10 percent bleach solution, and fill it with moist peat moss, fine vermiculite or seed-starting mix that has been sterilized in the microwave and allowed to cool.

Sprinkle the spores on the surface without covering them, since they need light. Close the box and set it in bright light, never in direct sun, at around 64–75 °F. After two to eight weeks a green film appears: tiny heart-shaped prothalli, which must stay moist to be fertilized. Thin the mat if it is too dense. The first true fronds show two to six months later; then move small clusters into individual pots and gradually accustom them to room air.

Common problems

• Yellow fronds, stalled growth: too much direct sun.
• Brown edges or tips: air too dry, mix allowed to dry out, or too much fertilizer.
• Large dead patches on fronds: fungal or bacterial disease taking advantage of a plant stressed by conditions it does not like.
• Root or crown rot: overwatering, a poorly draining mix, or water sitting in the center.
• Regular brown lines under the fronds: these are the sori, perfectly normal, not scale insects.
• Pests: scale, mealybugs, foliar nematodes and, outdoors, slugs and snails. Insecticides often damage this fern, so remove scale by hand instead.

A single symptom can have several causes: check light, moisture in the mix and the air, temperature and roots together before acting.

Toxicity

No toxicity has been reported: ferns like this one are considered safe for dogs and cats, and no human poisonings are known.