Java Fern Care, Reproduction and Fact sheet

Java Fern, or as it’s known to scientists, Microsorium pteropus, is in my eyes, the perfect aquarium plant and still my favorite. And this is coming from a person who keeps such beauties as Cryptocorne axelrodi and Bacopa carolina. Why do I think Java Fern is the perfect aquarium plant? Quite simply, because anyone can grow the darn thing (like algae) and it’s beautiful to boot (unlike algae). For those aquarists who have never experienced Java Fern, consider these features:

• It can be cultivated in tap water, dim or bright light, with or without gravel, fresh and brackish, soft or hard.
• It flourishes without added fertilizers or CO2.
• It is more snail resistant and actually grows better with higher fish loads.

Even if you’ve had trouble growing aquatic plants, you can probably grow Java Fern. Add to this a beautiful medium to dark green color with forms ranging from bushy to leafy spikes and you have what experts call a “beautiful” and “decorative” aquarium plant. Now that my shameless expounding is complete, we can describe the care and maintenance of this great aquarium plant.

Java Fern’s Place in the World of Plants

To understand why Java Fern is so hardy and easy to propagate is to understand the evolution of plants in general. For simplicity let’s group aquarium plants into three orders. In the lowest order is algae. Easily propagated by all aquarists (whether they want to or not) algae spores are carried through the air.

At the next level are non-flowering plants. In this primitive group, we find Ferns (such as Java and Watersprite), as well as mosses and minute floating plants such as Riccia. Many hobbyists may be surprised to learn that these plants not only reproduce vegetatively but like algae, also by spores carried by the wind.

The highest order of plants is flowering plants. This includes the popular aquarium plants including Echinodrous sword plants and Cryptocorynes. By now, you should realize that the difficulty in keeping many aquarium plants has much to do with their genetic simplicity.

So What is a Java Fern?

Java Fern is an amphibious jungle plant that grows attached to tree trunks, rocks, and the ground. It can be found growing on the waterline of mountain streams and waterfalls, as a wild grass in tropical rain forests, and even in coastal brackish areas. But unlike many other aquarium plants, it can prosper submerged indefinitely. Its growth is such that as old leaves grow tall and die, new ones have already stolen the spotlight. Java Fern (Microsorium Pteropus) is widely distributed in tropical Southeast Asia, especially southern China and the Indo-Malayan area (that includes the island of Java and the Phillippines). Java Fern has also been recorded in Japan and the Pine Barrens of the New Jersey coast. This later location supposedly hosts a different Microsorium variety.

I have also heard some hobbyists claim there is an African variety of Java Fern, although this may be a reference to another aquatic fern, Bolbitis heudeloth. Furthermore, a Malayan plant similar to Java is supposedly sold in shops. The hobbyists can distinguish this plant from true Java Fern by its thinner rhizomes and stems. A variety known as the “Windel v” is very attractive. These “other” Java Ferns may explain the recent discussions I’ve had with aquarists regarding different varieties of the plant. Hopefully, someday an article will appear which will clear up the nomenclature!

Java Fern is composed of three important parts. The roots of the plant are its most unique aspect. They appear to function not as nutrient carriers, but rather, as anchors. The roots are dark brown and hairlike and attach themselves to wood, gravel, and even rocks! This last anchor site still amazes me, since I have seen Java Fern become “stuck” to completely smooth stones. It is as if the roots become sticky, or find some way to adhere themselves to the seemingly smooth surface. The roots can become quite long when they are not attached. A Java Fern situated at the top of an aquarium can really “let its hair down” as it seems to “search” for an additional anchor site.

The heart of a Java Fern is its durable rhizome, which creeps in length and thickness with age, and eventually branches out to cover wider areas. A Java Fern on the end of a piece of 6″ driftwood will eventually make its way to the other side of the wood. This could take a year to accomplish, though, as rhizome growth is slower than leaf development.

The leaves of Java Fern are equally hardy. Healthy leaves are a stunning dark green with a leathery texture. A well-kept specimen can have a few leaves up to 10 inches long and 1.5 inches wide. It has been my experience that some plants tend to “stay low” in height as they branch out. This form is more like a bush. I have found that this characteristic develops in plants that are “floated” for a long time. By contrast, plants with thick rhizomes tend to develop a few tall, thick, “spiky” leaves. I think this may be a species difference.

Should you trim your Java fern?

Regardless of type, to encourage taller growth, new plants should be pruned so more energy is available for rhizome and leaf growth. Trust me – the leaves will come back, albeit taller. I have also seen shop varieties with trilobate leaves, but I have never, unfortunately, experienced these in my aquariums. This happens when the leaves are allowed to grow large.

Keeping Java Fern in Your Aquarium

With all its beauty and ease of propagation, I often wonder why Java Fern is not more frequently available in pet shops. It appears well-suited to the low-light and hard/alkaline conditions often found in dealer tanks. The slow growth of Java Fern could be a factor (fish farmers may be impatient too).

When you do find Java Fern, it may be planted in the gravel. Having a good idea of what Java Fern looks like before you ask for it helps a lot as many dealers are unfamiliar with the plant.

Keep Your Java Fern Submerged

When you buy Java Ferns I recommend you ask for them submerged in water. Dry air is the Achilles heel of Java Fern. This hardy plant needs to keep submerged all times. True it is most often found in the wild as an emersed plant, but as Yoshino & Kobayahi (1993) pointed out, it is most abundant in areas exposed to water sprays. The leaves of Java Fern dry quickly, so as you set up its new home, keep it submerged or use a spray bottle to keep the leaves moist as you prepare the tank.

Does it need to be planted?

To facilitate the acclimation of any new plant, I like to initially add a bit of electrolyte-based water conditioner, such as Jungle’s Plant Saver. After purchase, you now have the option of tying it down, planting the roots, or letting it float. The former method is preferred by me. I like to use black thread (which matches the roots) to gently tie down the rhizome to a piece of driftwood. Java Fern seems to grow best when attached to a nice piece of wood and given room to “spread.”

But there’s no harm in tying it to small scrap wood, ornaments, rocks, and gravel. It will grow well there too. Holding the plant down in the gravel by its roots can be cumbersome at first, but eventually, it will be anchored by its attachment to bits of gravel. Some people have had trouble acclimating to Java Fern initially. It has been suggested that this is often due to the fact that imported Java Fern is collected along with brackish coastal areas. However, it will rebound. You may want to ask your dealer where his stock is from and how long has it been in freshwater.

Since Java Fern is often found near moving water in emerged form, it likes swift oxygenated water during the evening (hence, the leathery leaves). This is usually no problem in the home aquarium, where powerheads and filters increase oxygen saturation. This is a refreshing change from dealing with flowering plants in search of lots of CO2, which is often not available in large enough quantities in home aquariums.

Water Temperature

Java Fern accepts a broad range of water temperatures from the mid-60s to the mid-80s, but is best at temperatures in the mid-70’s. Yoshino & Kobayahi, in their classic Natural Aquarium: How to Imitate Nature in Your Home (1993), report on a peculiar disease affecting aquatic ferns during periods of high water temperatures. They advise that tank temperatures do not exceed 82 degrees and that any dying leaves or runners be pruned. However, I have never experienced this disease with my Java Ferns in the 4+ years I have grown them. And this includes the usual Jersey summer when my Java Fern tank stays in the mid-80’s for weeks at a time. Perhaps I have been lucky. Water hardness and pH ranges are equally liberal.

Java Fern pH range

Java Fern is found on jungle floors where soft, acidic water sprays on its leaves, on the edge of mountain streams where near neutral conditions exist, and in the hard, alkaline tanks of African Cichlids keepers who use it as their plant of choice. Aggregate recommendations for Java Fern range from a 5.0 to 8.0 pH with a 2-25 DH. Here in New Jersey, my tap water ranges from 6.6 to 7.8, with a German hardness of 10 DH and my Java Fern grows fantastic. Most experts recommend optimum conditions at a pH of 6.0 to 7.0 with hardness from 2-12 DH.

Lighting: do java ferns need a lot of light?

Lighting for Java Fern is similarly easy. Java Fern does well in subdued to bright light, and unlike other aquarium plants, even seems to prefer more dim conditions. One fluorescent strip light sized over your tank is plenty. In my Java Fern tank, one side is exposed to diffused morning sun from an adjacent room.

The ferns really respond well on this side of the tank. I use a trace fertilizer occasionally for the minute amount of potassium required by the fern, or when I see the leaves yellowed, which is a rare occurrence. If you have an ungraded gravel bed, you may want to occasionally use an ion-exchange resin such as Aquarium Pharmaceutical’s Phos-Zorb to take care of phosphate build-up. But these are routine practices for generally planted tanks. Java Fern is most forgiving in these areas.

Does Java fern absorb ammonia?

Java Fern is an efficient utilizer of ammonium products ( the preferred nutrient of plants). So unlike the usual recommendation for planted tanks, stocking levels for fish can be higher without detriment to the plant. Ammonium is in smaller quantities in alkaline tanks (where ammonia is more produced as the first step in the nitrogen cycle) but my Javas still do quite well in my alkaline tanks.

Plant Companions

A good geographic aquarium display using Java Fern could include fish that also prefer cooler, oxygen rich waters. China’s Golden Barbs such as Barbus semifascioltus or schuberti, Spanner Barbs from Java (B. lateristriga), or Black-Spot (B. filamentosus), Purple-Headed (B. nigrofasciatus), or Cuming’s Barbs from the Sri Lanka mountains would all be geographically appropriate.

An aquarium manual some years ago briefly mentioned that a scat ate the leaves of a Java Fern and died. Since then there have been numerous reiterations of this tale with the conclusion that Java Fern is poisonous. The only fish I have seen eat a Java Fern was a team of hungry Goldfish – and they all lived. Clearly this theory needs scientific substantiation.

Aside from the pruning strategies already mentioned, your Java Fern will now pretty much take care of itself. It is an extremely economical plant. I have filled up many tanks from just one small plant I received a few years ago. And that’s without extra lighting or gravel or CO2 canisters. With Java Fern any hobbyist can have a beautiful planted tank. Even impatient ones.

How do Java Ferns reproduce?

Java Ferns’ reproductive flexibility is one of its great strengths. Aside from airborne spores (which are supposedly rare even in nature), I have found four (4) ways new plants or leaves develop in the home aquarium. One is through the ever-creeping rhizome, which sprouts new leaves as it grows in width and length. A second is through the development of tiny plantlet “babies” at the tips of other leaves. This is especially common with leaves that are long or older. Eventually, the plantlet grows to about 1 inch and breaks off the mother leaf. This is similar to how Watersprite (Ceratopteris sp.) reproduces, which is in the same family of ferns. “Impatient” aquarists can break off the plantlets early without any harm to either plant.

Two other methods of Java Fern reproduction are less frequently described. In fact, I have yet to read the descriptions. I have observed that older leaves of Java Fern, as well as large leaves that are transplanted, often develop black “spore” spots on the underside. You can anticipate this when a leaf looks weathered, with more pronounced vein lines. These spots eventually develop into plantlets, and it has been my experience that these plantlets usually grow quite large and hardy. In fact, they must be broken off manually. It is as if a dying Java Fern leaf wants to “go out with a bang!” One leaf on a plant I had was torn and decayed but still produced babies for a year until I pruned it.

The last method of Java Fern reproduction I have witnessed involves plants growing from the roots. This only happens when the roots are hanging in the water without attachment. I cannot find any documentation of this reproductive method, but nonetheless, I have witnessed it. It makes for a very attractive cascading effect, almost like a hanging houseplant. Recently I discovered little Javas growing inside a cave from the driftwood in my tank. I am not sure if these are from adjacent roots which made their way into the cave, or by spores!