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Crocodile Fern: The August 2022 Houseplant of the Month

The crocodile fern or alligator fern (Microsorum musifolium) is a relatively recent addition to the houseplant galaxy. It really wasn’t widely available until someone, back in the 1990s I’d guess, noted the intricate dark sunken veining on the midgreen leaf. They felt it looked like the scales on a crocodile’s back, so they began selling it as the crocodile fern. To reinforce their promotion, they then invented the very scientific-sounding cultivar name Microsorum musifolium ‘Crocodylus’.

Close up leaf showing the scalelike arrangement of the veins.
The intricate veining suggests the scales on a crocodile’s back. Photo: David Stang, Wikimedia Commons

Apparently, a plant with a name like crocodile fern has great sales potential. One known as banana-leaf fern, based on its botanical epithet (that’s what musifolium means), not so much. So, with its new name, crocodile fern, the little-known tropical plant set out to conquer the houseplant world… And has pretty much succeeded, as you find it almost everywhere.

Today, we know the name ‘Crocodylus’ is illegitimate. A cultivar name implies a plant is different from the wild form. This plant is not. It’s just a plain Microsorum musifolium. If your label indicates ‘Crocodylus’, you can strike that. But the common name crocodile fern will probably carry on.

Family Background

The genus Microsorum is a genus of nearly 50 tropical and temperate ferns found in the Old World, mostly Asia and the Pacific islands, with outlying species in Africa and northern Australia. They’re sometimes called wart ferns.

The name Microsorum means “small sorus,” a sorus (plural sori) being a spore-bearing structure.

Microsorum is occasionally spelled Microsorium, but the added “i” is incorrect.

Microsorum ferns often have simple tonguelike fronds, like M. musifolium, but some have divided ones, looking more like our image of a fern. The fronds grow from hairy rhizomes that can be long or short, the latter being the case for the crocodile fern, whose rhizomes are so short as to be barely noticeable. Mature specimens produce rows of small sori on the underside of the frond.

A Houseplant Straight from the Jungle

Maps showing original distribution of the crocodile fern.
:Crocodile fern grows wild in Southeastern Asia. Photo: powo.science.kew.org

The crocodile fern is native to Southeastern Asia, from Myanmar to New Guinea. It grows in forested areas in moderate to deep shade.

Crocodile fern growing as an epiphyte.
Crocodile fern usually grows as an epiphyte, pressed up against the trunk of a tree. Photo: powo.science.kew.org

It is essentially an epiphyte, usually growing well off the ground attached to a tree trunk or branch. Occasionally it can be a lithophyte, growing on rock walls. It can even be terrestrial, usually when an established plant is knocked free of its aerial perch and continues to live on the ground.

It adapts perfectly well to growing in pots.

Trash-Basket Plant

Trash-basket plants catch falling debris and use it for their growth. Photo: Flickr

The crocodile fern is a trash-basket plant. The plant presses up against a tree trunk, forming a half-basket of fronds that catch falling leaves and other debris. They slowly decompose and fertilize the plant, plus hold moisture it can absorb. In a pot, with no trunk, it will form a full circle, much like a bird’s nest fern (Asplenium nidus and others).

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Giant crocodile fern
Crocodile ferns can become huge over time. Photo: n1gardencentre

The fronds start small, often less than 8 inches (20 cm), but then lengthen. Expect them to reach 2 feet (60 cm) long in the home, often giving a plant about 3 feet (90 cm) tall and wide. They reach twice that in the wild.

I’m sure this size is a not necessarily wanted by all plant owners. They discover only by growing one that their cute little fern is only a baby. It becomes quite large over time. And frond length is variable, growing longer under high humidity, shorter when air is dry. Since humidity levels in the average home vary, that usually makes for a plant with a very irregular form.

Sori on the underside of a crocodile fern frond.
Home gardeners rarely see their crocodile fern produce spores. Photo: Agnieszka Kwiecie?, Nova, Wikimedia Commons

There are no flowers: ferns simply don’t produce them. But then, you’ll probably never see spores either. The sori needed to produce spores need really high humidity. Since the air in our homes is inevitably on the dry side, less than 70%, sori are therefore usually absent from indoor crocodile ferns. Only in extremely humid greenhouses—or specimens growing outdoors under humid tropical conditions—are they usually seen.

Related Plants

Elkhorn fern with crested leaf tips.
Microsorum punctatum ‘Green Flame’. Photo: Katherine Wagner-Reiss, Wikimedia Commons

The only other Microsorum you see used as a houseplant is the elkhorn fern (M. punctatum), a similar trash-basket species, but with longer fronds and without the reticulate veining. There are all sorts of cultivars with crested frond tips, like M. punctatum ‘Grandiceps’, ‘Cristatum’, ‘Green Flame’ and ‘Serratum’. They are popular among serious fern collectors, but need too much humidity to do well in the average home.

Kangaroo fern with shiny leaves.
Kangaroo fern (Zealandia pustulata). Photo: Vi?ctor Sua?rez, depositphotos

The kangaroo fern was a Microsorum for a few years under the name M. pustulatum, but has moved on to a new name: Zealandia pustulata. It has also been Phymatosorus diversifolius and Microsorum diversifolium, among others. This is indeed a tough-as-nails houseplant fern, but, with its pinnate (lobed) fronds on petioles widely spaced on long rhizomes, doesn’t look much like the crocodile fern.

Bird’s nests ferns (Asplenium nidus and others) are, like the crocodile fern, trash-basket plants, and may look superficially like them, but belong to a different branch of the fern division.

Caring for a Crocodile Fern

Growing a crocodile fern to perfection can be a challenge, but just growing one that takes on the normal irregular form of the species is actually quite easy. It really is an easy houseplant to grow!

Light

The crocodile fern does fine in partial shade and even deep shade. However, it can tolerate much more light than many specialists’ claim, even full sun. You just have to acclimatize it and keep up the humidity. So, essentially, almost anywhere in your home offers light enough for this plant.

It does like a summer outdoors, but do acclimatize it to outdoor conditions before putting it in the sun.

Watering

It prefers soil that never fully dries out, yet, starts to. So, wait until it starts to feel a bit dry to the touch before watering thoroughly.

Atmospheric Humidity

High humidity is definitely best. The brown markings, dry edges, wavy edges, shortened fronds and other anomalies people find in their crocodile fern are all due to irregular humidity.

Crocodile fern showing leaf damage due to dry air.
Dry air causes damage to delicate fronds: brown marks, irregular growth, damaged frond tips, etc.. Photo: stg809, reddit.com

Yes, it will survive fairly dry air, but its appearance will take a hit. Strive for 70% atmospheric humidity with this plant. And 80% is better. That said, you can keep yours in reasonable condition, with only minor damage, at 60% atmospheric humidity. That’s a lot, but still doable.

No, spritzing it with water won’t help in the slightest. Nor is a humidity tray (pebble tray) alone going to be enough.

Actually, almost all your houseplants will enjoy the benefits of a humidifier, not just your crocodile fern. Photo: Dimaberlin, depositphotos

You pretty much have to use a humidifier and a dedicated plant room—where humidity is allowed to soar!—to grow this plant to perfection in the home.

Place your crocodile fern inside a sealed transparent plastic bag for the winter to keep it in top shape. Ill.: Claire Tourigny, from the book Les 1500 trucs du jardinier paresseux

If a humidifier isn’t doable, try bagging it for the winter (the dry air season indoors). Read Bag Delicate Houseplants for the Winter for more information.

Helpful Hint

A crocodile fern will soon take over the average terrarium. Ill.: Horticus & Amazon.ca

Some so-called houseplant experts recommend this fern as a terrarium plant. Well, that would work when it comes to humidity, as terrariums certainly do provide a humid environment! However, these are people who sell terrariums, not people who grow terrariums. Because this fern gets so big so fast, it will likely outgrow a terrarium home within months. And extracting an overgrown plant from a terrarium is nobody’s idea of fun.

My suggestion. Use something smaller in your terrarium … unless yours is really huge!

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Fertilizer

Feed lightly, if at all, in spring or summer. Any fertilizer will do. Like many epiphytes, this plant is quite capable of getting along with few minerals.

Weather Icons

Temperature

The crocodile fern is a tropical plant and prefers warm temperatures year all year long. A range between 65°F (18°C) and 75°F (24° C) would be perfect. It will tolerate more heat as long as it is accompanied by good humidity. Try to avoid temperatures below 50°F (10°C); they can cause permanent damage.

A winter somewhat cooler than the summer is not a problem as long as the plant remains within its usual limits.

Repotting

Like many epiphytic houseplants, this fern gets along fine in a small pot, as long as you keep up the watering needed (small pots dry out more quickly). You can repot every 2 or 3 years, preferably in spring or summer. In doing so, replace most of the old potting mix, which tends to accumulate too many minerals over time.

Generic potting soil, both well drained, yet holding some humidity, would be fine, but if you prefer orchid mix, that would work too.

Usually, you simply pot up into a slightly larger pot, but you can also choose to divide your plant at this time. If you divide, you might need 2, 3 or more smaller pots. For that, see Multiplication.

Grooming

First, do expect older fronds to turn yellow, then brown. When they do so, just clip them off at the base. That’s just part of life for this plant!

Bumps, bruises and dry air cause brown marks, irregular edges and shortened frond tips. That’s something you can’t remedy quite so rapidly, as the rest of the frond is still green and useful to the plant. You can prune off the brown bits, but … generally, keep the humidity up, up, up and you’ll largely avoid the problem.

Multiplication

If you find a source of spores, you could multiply your crocodile fern by sowing them. But spores are hard to come by. (If you do have access to a few, here’s what to do: Grow Your Own Ferns… From Spores!)

Usually, people simply divide their crocodile ferns and that is certainly easy enough. Each frond is attached to a short section of rhizome and fully able of growing on its own as a separate plant. So, simply remove the pot and pull or cut anywhere in such a way as to separate the root ball into 2, 3 or more parts, each with its own bit of shared earth and rhizomes. Then repot the division at the same depth as it was originally. Finally, water thoroughly, of course.

If you take a large division, it’s best to remove a few older (lower) leaves at the same time.

I find larger divisions look awkward for a long time, as all their growth is on one side at first, making them very lopsided. It takes ages for any symmetry to return. So, smaller divisions, or even just a section of rhizome, may be a better choice, as they’ll fill in their smaller pot more quickly and, with smaller leaves, won’t look as off-centered.

Problems

The main problem is brown frond tips and edges, mostly due to low humidity. Mealybugs and scale insects can be a concern, one best avoided by isolating new plants at purchase time. Insecticidal soap can help treat them.

Toxicity

The crocodile fern is not known to be toxic to either humans or their pets.


The crocodile fern: beautiful and intriguing, but not really so crocodilian, as there’s no bite behind this charming, easy-to-grow houseplant.

Garden writer and blogger, author of more than 60 gardening books, the laidback gardener, Larry Hodgson, lives and gardens in Quebec City, Canada. The Laidback Gardener blog offers more than 2,500 articles to passionate home gardeners, always with the goal of demystifying gardening and making it easier for even novice gardeners. If you have a gardening question, enter it in Search: the answer is probably already there!

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