It is well known that the Java Fern has different “varieties” — such as “trident”, “Windelov”, “Narrow Leaf” and “Needle Leaf”.
I kept normal Java Fern, as well as “Narrow Leaf” Java Fern in Singapore, at a temperature of around 29 to 30 degrees Celsius (85-86 Fahrenheit).
I found that the Normal Java Fern does well (nice green color, and grows baby plantlets), but the “Narrow Leaf” Java Fern does not do well (becomes browner and even blacker by the day).
I checked online and at least four other people have experienced this:
I think cooler temperatures might be the answer. My narrow leaf in syd are lush green and pearling like mad in temps of 25 celsius. In KL, 28-29 celsius, they grow a little, turn brown sometimes and are a bit of a hassle to keep. My normal java fern does well in any temps/conditions, just the narrow leaf, more demanding. Has anyone grew nice long narrow leaf in warm temps? Those in LFS have them in air conditioned rooms.
Narrow Leaf Java Fern does better in cooler temperatures (around 25 degrees Celsius)
Other anecdotal evidence that Narrow Leaf Java Fern may do better in cooler waters:
I’ve had a lot of success with Java Ferns and Narrow Leaf Java Ferns (NLJF) in my tank.
My tank is high-light (288Watts for 80gallon) and has lots of CO2 (3bps). I dose it with TMG almost every week. I tie the JF on driftwood and also bury them in my substrate, either way it grows well. Kwek Leong did share with me that growing them in substrate will produce longer leaves for NLJF and that holds true in my tank. I place them very new my water outlet as I read somewhere that the JF thrives in that environment. Also, I have a chiller that keeps my water temp at around 24.5-25.0C.
Hope this helps!
I knew of a tank that grow Narrow Leaf Java Fern very well and the conditions are like what Roger has too. Under these conditions, they grow very rapidly and the leafs are jade green and very clean (no spots at all).
Yet another post:
I used to have prolific growth of Narrow Leaf Java Ferns in my tank. I don’t think CO2 injection is necessary but the ferns probably do better under low light and cold water.
Methylene Blue and Narrow Leaf Java Fern
Something else interesting that I found out is that methylene blue seems to affect narrow leaf Java Fern negatively, but not normal Java Fern. Basically, the Methylene blue seems to stain the narrow leaf Java Fern, and lead to its demise. I tried this out inadvertently while dosing my fish tanks with methylene blue to cure ich.
The Narrow Leaf Java Fern is on the right of my fish tank in the video below (it was still in an ok state at that time):
I think the conclusion is that Narrow Leaf Java Fern is a slightly more demanding plant when it comes to temperature (does not do well above 27-28 Celsius). Due to global warming, many countries in the tropics are now stuck with 30 degrees Celsius temperature almost all year round, hence the normal Java Fern may be a better choice.
It also sort of makes sense in terms of plant biology. Usually plants with “thin” leaves tend to be those that live in colder/cooler weather such as pine trees. While plants with big wide leaves are those that live in hot tropical weather (such as banana tree). Using this “logic”, I would suppose that needle leaf Java Fern also does better in cooler waters.