you don't need CO2 to grow java fern, it's one of its many charms . . . I've grown it by the bushel in low-light tanks w/o CO2
that being said, it should be fairly easy to grow java fern on driftwood, so it might help if you told us what lighting you have, what your water parameters are, and if you use any fertilizers or other supplements
note: since java fern gets its nutrients from the water column, your water conditions and fertilizer info can be particularly relevant