No, Java fern doesn’t need to be planted. In fact, you shouldn’t plant a Java fern at all. If its rhizomes get buried in the substrate, the fern won’t be able to absorb any nutrients. Eventually, the Java fern will stop growing, rot, or slowly die, so letting your Java fern float in the water is better.
Because this hardy plant doesn’t require any substrate, it’s perfect for bare-bottom tanks. You can just let your Java fern float around in the tank.
But because this plant is usually found growing on rocks and plant roots in the wild, attaching it to rocks, wood pieces, or decors in the tank is recommended. You can use a zip tie to do this; just remember to remove the zip tie once the fern is firmly attached.