Quick answer: Attach Java fern to wood or rock and keep the thick rhizome uncovered. Give the plant low light and skip extra CO2 in a basic tank. Split the rhizome later when you want more plants.
Java fern is a low-light rhizome plant; Tropica lists it 15–30+ cm tall and says a covered rhizome will rot. This page is a grower-card comparison from Tropica, Dennerle Plants, and Aquarium Co-Op.
We only used live SKU cards that list light and CO2 plus a size or placement number.
That selection rule kept this guide on named products still sold as Java fern or a named Microsorum pteropus form. Our research team compared six maker pages and skipped unnamed bunches, mystery cups, and blogs with no care card.
The six cards do not use the same units, so we kept each maker’s own labels. Tropica prints a Low light mark and defines medium light as 0.5 W/L.
Aquarium Co-Op prints 10–20 PAR on its Java Fern card, and Dennerle Plants prints medium–low. Tropica’s Windeløv and Narrow cards list 10–20+ cm after two months, while the classic Tropica card lists 15–30+ cm.
Dennerle Plants lists the main form up to 40 cm and lists Trident up to 30 cm. That spread is why this page is a comparison, not a ranked list.
Pick the form that matches the space you have, or start from our list of low-maintenance planted aquarium plants for beginners.
Attach Java fern so the rhizome stays open
The thick green runner must stay open to the water, or Tropica says it will rot.
That runner is the rhizome, and both leaves and thin roots grow from it. The roots can grip wood or stone, but the rhizome is not a buried root ball.
Tropica’s classic page says grow it on a root or stone and attach it with fishing line until it holds. If you set it on the bottom, do not cover the rhizome.
Aquarium Co-Op’s Java Fern page says the same risk in other words: do not bury the rhizome or the plant may suffer. Use one of these attach methods from those pages:
- Tie the rhizome to wood or stone with fishing line, as Tropica describes.
- Press the thin roots onto decor with gel glue, as Aquarium Co-Op describes.
- Wedge a small clump into a rock crack, as Aquarium Co-Op describes.
Aquarium Co-Op’s page also gives a time for glue. Draw a small line of gel, then press the roots for 30 seconds or until the gel sets.
Keep these parts uncovered:
- The thick green rhizome
- The bases of the leaves
- New plantlets on old leaves
You can hide the thin roots in a crack, but do not pack gravel over the runner. If you already buried a clump, lift it, rinse the grit off the rhizome, and tie it again.
Trim only leaves that are already dead, and leave fresh green fronds on the open runner.
Light and CO2 numbers from the grower cards
All six cards list low light, or they list no extra carbon.
Tropica marks classic Java fern, Narrow, and Windeløv as Low light. The same Tropica cards define average medium light as 0.5 W/L and mark CO2 as Low.
Those Tropica cards define a medium CO2 need as 6–14 mg/L. They define a high CO2 need as about 15–25 mg/L.
Dennerle Plants lists light as medium–low for both the main form and Trident. Both Dennerle Plants cards list CO2 at 0–10 mg/l.
Aquarium Co-Op’s Java Fern page lists recommended light as low light at 10–20 PAR and lists the CO2 requirement as none. Comparing published specs, the cards agree you do not need a high-output lamp or a CO2 cylinder.
Aquarium Co-Op’s page also warns that too much light may burn leaves or grow extra algae. If the lamp is bright, move the fern farther away or shade it with taller plants.
A simple light plan from those cards looks like this:
- Start in the Low band Tropica prints, or in Aquarium Co-Op’s 10–20 PAR band.
- Skip added CO2 unless you already run it for other plants.
- If algae coats the old leaves, lower the light before you add more fertilizer.
Java fern is slow on every Tropica card we used, and slow leaves hold algae longer than fast stems, so low light is the control.
Six Java fern products by listed attributes
Listed height on these cards runs from about 10 cm to 40 cm.
Our research team pulled only attributes the maker printed, so this table has no rank column and no price column.
| Product | Listed form | Listed height | Light on the card | CO2 on the card | Growth on the card |
|---|---|---|---|---|---|
| Tropica Microsorum pteropus (item 008) | 5 cm pot | 15–30+ cm after two months | Low | Low | Slow |
| Tropica Microsorum pteropus ‘Narrow’ (item 008A) | 5 cm pot | 10–20+ cm after two months | Low | Low | Slow |
| Tropica Microsorum pteropus ‘Windeløv’ | Patented cultivar | 10–20+ cm after two months | Low | Low | Slow |
| Dennerle Plants Microsorum pteropus | Background fern | Up to 40 cm | Medium–low | 0–10 mg/l | Slow–moderate |
| Dennerle Plants Microsorum pteropus ‘Trident’ | On wood or rock | Up to 30 cm | Medium–low | 0–10 mg/l | Slow |
| Aquarium Co-Op Java Fern | Attach to hardscape | Height not listed | Low light, 10–20 PAR | None | Slow grower |
Tropica’s classic page says the plant is a water fern from Asia, 15–30 cm tall, sold in a 5 cm pot.
Tropica also used this form in layouts of 100 L, 112 L, and 128 L.
Tropica’s Narrow page says the leaves become 10–20 cm and the rhizome is 10–15 cm or more. The pot size is also 5 cm, and Tropica says Narrow suits smaller aquariums.
One Tropica layout with Narrow is 46 L, and another is 54 L. That is the smallest printed layout size in this set of cards.
Tropica’s Windeløv page says the form becomes 15–20 cm tall and wide. Tropica names it after founder Holger Windeløv and calls it a patented variety.
Tropica used Windeløv in 54 L layouts and in a 300 L layout.
Dennerle Plants lists the main form as a background plant up to 40 cm, which is taller than Tropica’s 15–30+ cm band. Dennerle Plants lists Trident up to 30 cm and places it on wood or rock.
Aquarium Co-Op does not print a height in centimeters, but that page does print 10–20 PAR and a CO2 value of none.
Water, fertilizer, and gravel around the fern
Dennerle Plants prints a temperature and pH band, and the three Tropica cards we used do not.
Both Dennerle Plants cards list 22–28°C, which is about 72–82°F. Both list pH 5–8 and water hardness from very soft to hard.
Both Dennerle Plants cards name the family Polypodiaceae and list origin as South East Asia. Tropica’s three cards still help on water because they call the classic form hardy in all conditions.
Tropica also tells you the black spots under leaves are sporangia, not disease. Leave those spots alone unless the leaf is already dying.
Aquarium Co-Op’s Java Fern page treats brown leaves as a possible nutrient gap. That page says to dose liquid fertilizer until the water reads 20–50 ppm nitrate.
If growth stays poor, that page says to add extra potassium on top of the all-in-one dose. Java fern feeds from the water, not from a buried root tab.
For mixes and dose styles, see our desk on the best aquarium plant fertilizer.
A simple feed plan from those cards looks like this:
- Keep the rhizome in open water so it can take nutrients.
- Dose a complete liquid if leaves thin or brown, as Aquarium Co-Op describes.
- Watch nitrate on a test strip and stay in the 20–50 ppm band Aquarium Co-Op prints.
- Add extra potassium only if that first step fails, as that same page says.
Gravel still matters for the rest of the tank, but it does not feed this fern, so do not bury the runner in it.
If you keep swords or crypts nearby, pick a bed from our best aquarium gravel for plants guide. Leave a bare wood or stone patch for the fern.
Aquarium Co-Op says Java fern can often survive with goldfish and African cichlids, but those are maker claims, not tank trials from this desk.
How to propagate Java fern
You make more plants by splitting the rhizome, or by waiting for plantlets on old leaves.
Tropica’s classic page says it is easy to propagate by splitting the horizontal rhizome. Aquarium Co-Op’s page says cut the rhizome and split it into two plants.
Dennerle Plants says older leaves can make plantlets that you cut away and tie with thin fishing line. Aquarium Co-Op adds a leaf method that uses the dark dots on a trimmed leaf.
Use this split method when the runner is long:
- Lift the clump from the wood or stone.
- Cut the rhizome with sharp scissors so each piece has leaves.
- Keep each piece’s rhizome uncovered.
- Tie or glue each piece as you did the first plant.
Use this plantlet method when old leaves show dots:
- Wait until a plantlet has its own small roots.
- Cut it free, as Dennerle Plants describes.
- Tie it with thin fishing line.
- Leave the parent leaf if it is still green.
Do not bury the new pieces, because a new plant has the same rot rule as the parent. Tropica’s Narrow card helps you plan space after a split, since leaves stay 10–20 cm.
The Narrow rhizome can run 10–15 cm or more, and Windeløv stays 15–20 cm tall and wide on Tropica’s page. The Dennerle Plants main form can reach 40 cm, so leave room for the form you bought.
FAQ
Can I bury Java fern in aquarium gravel?
No, Tropica’s plant page says a covered rhizome will rot, and Aquarium Co-Op’s page says the plant may suffer if you bury that runner. Tie it to wood or stone instead, or set it on the bottom only if the rhizome stays open.
How much light does Java fern need?
Tropica lists Low light on the three forms we used and defines medium light as 0.5 W/L. Aquarium Co-Op lists 10–20 PAR, and Dennerle Plants lists medium–low. Start in that low band, and raise light only if new leaves stay pale and algae is not already coating the old ones.
Does Java fern need CO2 injection?
These cards do not require CO2 injection. Tropica marks CO2 as Low, Dennerle Plants lists 0–10 mg/l, and Aquarium Co-Op lists none. Added CO2 is for other plants in the same tank, not a Java fern rule.
Why are there black spots under the leaves?
Tropica says those spots are sporangia, the plant’s reproductive organs, and they are not a disease sign. Aquarium Co-Op also describes dark dots that can grow into plantlets. Leave healthy spotted leaves in place unless a leaf is already dying.
How tall will Java fern get?
Tropica lists the classic form at 15–30+ cm after two months. Narrow and Windeløv are listed at 10–20+ cm on Tropica’s cards.
Tropica also says Windeløv becomes 15–20 cm tall and wide. Dennerle Plants lists the main form up to 40 cm and Trident up to 30 cm.
What temperature and pH do the cards list?
Only Dennerle Plants prints those numbers on the two cards we used, and both list 22–28°C and pH 5–8. Tropica’s three cards do not print a temperature or pH band. If you need a printed range, use the Dennerle Plants figures and keep the rhizome uncovered.
How do I attach Java fern without killing it?
Use Tropica’s fishing-line method or Aquarium Co-Op’s gel-glue method. Press glued roots for 30 seconds, as Aquarium Co-Op states, and keep the thick rhizome out of the gravel. Split the runner later if you want a second clump.
