Filmy ferns are very enticing horticultural subjects, and are sure to become a weakness of many rare miniature plant addicts. Part of what makes them so alluring is their unique frond shapes and textures, as well as their semi-translucent leaf tissue which makes them look like living gems. Let’s learn more about these amazing plants, and how to grow them….
About Filmy Ferns
Filmy ferns occupy a number of genera, including but not limited to Hymenophyllum, Trichomanes, and Crepidomanes. The approximately 650 species are extremely varied in frond form, size, and growth habit. Some species are no larger than ¼” tall, and others have fronds much larger. The fronds may be entire, as a disc or fan, or intricately divided and feathery. Fronds come in a wide spectrum of colors, with most being shades of green, but some may have a glaucous appearance. Most have tissue which is only one cell thick, making it translucent to some degree, and earning them the “filmy” moniker.
Diminutive filmy ferns create fine carpets along horizontal or vertical surfaces, and large species create clumps and draperies on trees and rock faces.
Filmy ferns’ environment is usually very wet, often in cloud forests and fog prone locations, as well as rainforests with significant precipitation, which maintain the humidity levels and generally cooler temperatures necessary for their survival. They grow in areas where they are sheltered from dry air, such as pockets of moss, wet wood, and rock crevices. The plants may also be near splashing, dripping, or seeping water, which supplies constant moisture to their delicate fronds, and creates a protective barrier against air movement.
How to Grow Filmy Ferns
Most filmy ferns will require different growing conditions than the majority of other tropical plants which you may want to grow. Therefore, you’ll need specialized growing tanks solely for filmy ferns and other plants and bryophytes which do well in similar conditions.
With this in mind, let’s take a look at some culture tips for these delightful but challenging plants.
Humidity and Moisture
Filmy ferns require exceptionally high humidity, as would be found in their natural habitat. They have evolved to be adapted to these conditions, which is why their fronds are extremely thin (“filmy”) and have little to no cuticle:
In layman’s terms, the quote above means that, similar to mosses, filmy ferns have adapted to utilize their environment as way to maintain tissue hydration, as opposed to having structures or mechanisms for doing so within their foliage.
Since their leaves are so susceptible to drying out in the absence of moisture, you need to keep the humidity as high as possible. A Relative Humidity (RH) of at least 90% may be necessary to prevent desiccation, with higher RH being helpful.
Filmy ferns should be kept in extremely moist or wet conditions, which helps maintain high humidity and can also support tissue hydration by direct contact. Their rhizomes should never be allowed to dry out, and should be constantly in contact with, or covered by very moist or wet substrate. Many species benefit from frequent misting with pure water, which mimics their natural habitat.
Air movement should be avoided as much as possible. Even under humid and wet conditions, sometimes filmy ferns will dry out when exposed to air flow, even if it’s not directly blowing on the fronds. It’s best not to have fans in a filmy fern growing container, although in some cases you can pull it off if done thoughtfully and carefully.
When growing filmy ferns in a grow tank fans, you can use fiberglass window screen to reduce air flow over the fronds, as well as to hold in humidity and soften the lighting (see accompanying images).
If you must use fans, you can try using a digital timer with multiple on-off programs per day, so the fans are not on constantly.
When using fans, the ferns should be misted with distilled or RO water at least once a day to rehydrate any desiccation caused by the air movement.
As can be deduced by the humidity, moisture, and air flow sections of this article, filmy ferns should be kept in an enclosure which is entirely, or mostly sealed. Glass aquariums, jars, plastic tubs, and deli cups are good options.
Never use tap water for filmy ferns. Only use distilled or RO water, which mimic the purity of rain and mist from their natural habitat.
The best substrate will depend on the natural habitat of the species, though in most cases sphagnum moss will be an excellent choice. As mentioned previously, the rhizomes should be covered by, or at least in constant contact with very wet substrate.
Filmy ferns should not be planted in open spaces. They should be placed in sheltered locations, where wood, rocks, moss, and other surfaces will protect them from air movement and bright light. They will benefit from having their fronds close to, or partially enveloped by wet substrate and hardscape elements. Basically, the more sheltered you can make them, the happier they will be.
Do not plant filmy ferns high up in a tank, where they will be too close to light, heat, air movement, and other conditions that will harm them.
You may experiment with growing filmy ferns near water features, such as waterfalls and pond banks, where the rhizomes and fronds will receive constant moisture and humidity.
Filmy ferns can be grown on horizontal or vertical surfaces, though each species may have a preference. Keep in mind that vertical surfaces are more challenging to keep saturated.
Smaller species do well when partially enclosed in pockets and walls of sphagnum moss, which maintains high humidity in the direct vicinity of the fronds, and also may offer moisture to those which directly contact the wet substrate.
Some species of filmy ferns grow in areas where water is constantly flowing over the plant, or where the entire plant is seasonally flooded – you can experiment with growing them submerged in water. It’s important to use pure water, and to ensure that it stays fresh and does not stagnate.
If the species is suitable for growth under water, within a few weeks you should notice healthy new growth of rhizomes, and newly forming fronds. Aquatic leaves will usually be morphologically different from emersed leaves, and will die if taken out of water long enough to dry out completely.
Growing filmy ferns in water is a fun experiment, and when successful it results in beautiful and interesting growth. I’ve found that the growth rate under water is significantly faster than in terrestrial conditions.
Bright light should be avoided for filmy ferns.
The technical jargon quoted above can be translated loosely into layman’s terms to mean that lower light environments are more supportive of keeping filmy ferns hydrated.
Medium to low light, and indirect light, are ideal. Very shady spots are acceptable, but some species will grow substantially slower, or even stop growing if light is too dim.
Since filmy ferns grow in many different climates, there is not one global rule for temperature. Some prefer to be on the cool side, while others will do just fine in warm temperatures. If you know where a particular species came from, you can do some research to identify the ideal temperature ranges. When in doubt, intermediate temperatures are a good starting point. In general, you’ll want to avoid hot temperatures. In summery weather and hot locales, keep filmies in the coldest part of your home.
You can feed filmy ferns with liquid fertilizers at a very diluted strength, or a very gentle, slow-release pellet fertilizer, at a low dose. Use caution because some species may not fare well, and some fertilizers may do damage to the foliage. It’s best to start with extremely low doses and strengths, and test just a small portion of ferns. If they remain unharmed after several weeks, it should be OK to apply to the rest.
Some liquid fertilizers I have used are Grow More Urea-Free Orchid Fertilizer, and Sea Grow. They come as a powder which should be mixed with distilled water, to about 1/4 of the strength recommended on the packaging. Use a spray bottle to gently mist the plants every two or three weeks. A third fertilizer option is Osmocote Plus, a slow-release capsule. Use about 1 capsule per 4 square inches of fern clump. The capsules should release nutrients for 3-6 months.
Companion Moss and Plants
Protect small and micro species of filmy ferns from rampant mosses and plants, which will choke them out. Larger filmy ferns should be OK with moss growth, but keep it in check so it doesn’t get too out of hand.
Filmy Fern Growth Rate
Many filmy ferns are extremely slow growing, so patience will be necessary. As long as the rhizomes stay healthy, and proper conditions are met, they should plod along at their own pace.
When newly planted, they will take a long time to acclimate. After that, if no growth is seen for several months, but rhizomes are healthy, try increasing the light slightly, and possibly the humidity and moisture as well. It is advisable to alter only one condition at a time, to avoid shocking the plant, as well as so you can track how each change affects the plant.
Possible Problems with Filmy Ferns, and Their Causes
Fronds are turning a shade of black or brown, or have dark edges or patches.
Some possible causes:
- The humidity and moisture are too low
- There is too much air movement
- The temperature is too high
- The light is too bright
- A harsh fertilizer or chemical has been applied
- Inappropriate water was used (tap water, hard water, water with chemicals, etc)
- The fronds are old and are naturally dying as the plant puts out new growth.
Rhizome tips are no longer green, or rhizomes are dying
Some possible causes:
- The humidity and moisture are too low
- The rhizomes were allowed to dry out
- There is contamination from chemicals, pathogens, mold
- The substrate is too far degraded
- Inappropriate water was used
The plant is alive and healthy, but isn’t growing
Some possible causes:
- The plant needs more time to acclimate
- There isn’t enough light
- The plant needs more water
- There aren’t enough nutrients
There is mold on the substrate or otherwise in the container
Note that mold grows well in very wet and humid conditions, and therefore it is a common problem when growing filmy ferns. Most molds will not cause too much harm. Some more aggressive molds can smother and cause damage and decay.
Some possible causes:
- The substrate is degraded and decaying
- There is other decaying matter (dead foliage, dead rhizomes, etc)
- The substrate is too wet
- Temperatures are too high
- Ecosystem is out of balance
Treatment for mold:
- Replace the substrate when it breaks down and begins to mold
- Remove dead leaves, rhizomes, and other decaying matter
- Reduce substrate wetness
- Reduce temperatures to slow the mold growth
- Add microfauna, such as Dwarf White Isopods (Trichorhina tomentosa) and Springtails (Collembolla species)
As you can see, filmy ferns require extremely specialized conditions, and present a number of challenges in culture. Great care and patience will be required, but if you are successful, you’ll be rewarded with beautiful and unique plants that are a joy to behold.
- Michael C. F. Proctor, “Light and desiccation responses of some Hymenophyllaceae (filmy ferns) from Trinidad, Venezuela and New Zealand: poikilohydry in a light-limited but low evaporation ecological niche,” Annals of Botany, Volume 109, Issue 5, 1 April 2012, Pages 1019–1026, https://doi.org/10.1093/aob/mcs012
- “Hymenophyllaceae,” Wikipedia, https://en.wikipedia.org/wiki/Hymenophyllaceae
- Hymenophyllum nephrophyllum Kidney Fern Ship Creek Beach 2.JPG by MurielBendel licensed under the Creative Commons Attribution-Share Alike 4.0 International license and was modified with general enhancements for color and contrast. Description: Kidney fern (Hymenophyllum nephrophyllum) near Ship Creek Beach, West Coast, South Island, New Zealand.
- WP-Hymenophyllum-Exkursion nach Berdorf (Luxemburgexkursion) 011.jpg contributed by Oliver s. licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license and modified with general enhancements for color and contrast.
- Crepidomanes minutum utiwagoke01.jpg by Keisotyo licensed under the Creative Commons Attribution-Share Alike 3.0 Unported, 2.5 Generic, 2.0 Generic and 1.0 Generic license and was modified with general enhancements of cropping, color, and contrast.
- Filmy Fern (3162870189).jpg by Jason Hollinger licensed under the Creative Commons Attribution 2.0 Generic license and was modified with slight adjustments to contrast, color, and exposure. Description: Hymenoglossum cruentum (Cav.) C. Presl. 20090101 Parque Nacional Chiloe, Chile
- Hymenophyllum obtusum (palailaulii) (5868436134).jpg by John Game licensed under the Creative Commons Attribution 2.0 Generic license and modified by adjusting contrast, color, and cropping. Description: Hymenophyllum obtusum (palailaulii). Broader fronds and distinctively branched hairs help distinguish this small but attractive filmy fern from the related Hymenophyllum (Sphaerocionium) lanceolatum. The linear bright green fronds are the fern Adenophorus tenella. Epiphytic on a shady log, Poamoho Trail, Oahu.
- Mindo-Cloud-Forest-05.jpg used from Public Domain courtesy of Ayacop and modified with slight adjustments to contrast and color. Description: Cloud forest near Mindo, Ecuador
- Cloud forest panama 2.jpg contributed by DirkvdM licensed under the Creative Commons Attribution 1.0 Generic license and modified with adjustments to contrast and color. Photograph by Dirk van der Made (en:User:DirkvdM – for more photos see en:user:DirkvdM/Photographs). A cloud forest near Santa Fe, PanamÃ¡, April 2004.
- Monteverde Reserve Costa Rica 17.jpg by Cephas licensed under the Creative Commons Attribution-Share Alike 4.0 International license and modified with slight adjustments to color and contrast. Description: Monteverde Cloud Forest Reserve, Monteverde, Costa Rica