From my reading here on TFF it is perfectly OK to fishless cycle with live plants and in fact there may be positives to it. Note that rdd1952, the writer of the TFF fishless cycling pinned article usually does his cycling with plants and has had many documented successes.
Pros:
1) The live plants and the aquarium water on them from the previous tank they were in and the biofilm on them may be an "introducer" of a small amount of the correct bacteria needed for cycling, almost like a very small shot of mature media. (Note: this is pure speculation and I don't mean to spread false information. It is unproven as far as I know but seems possible.)
2) You get a chance to work on your plant arrangement and have something to do during the long weeks of fishless cycling.
3) You have a reason to turn your tank lights on and possibly enjoy the look of your tank even though you don't have fish yet.
4) The ammonia, nitrites and nitrates and warmer temperature shouldn't bother the plants at all and in fact it may even be a bit positive for their environment.
Cons:
1) Many people get extensive algae growth during fishless cycling and it gets all over the plants and is bothersome to get off. Many describe long hairy brown algae as being common and quite obnoxious to look at, counteracting the enjoyment of looking at your fishless cycling tank!
2) To have plants you usually have substrate (gravel or sand) and that too can get clogged with algae and be hard to clean at the end of cycling.
3) If you have a lot of plants they can consume quite a bit of ammonia and/or nitrates, even making the first stage of cycling extremely slow as there might not be enough ammonia left to sustain growth of the bacteria in the filter (this would have to be an extremely heavily planted tank I speculate.) Even a smaller number of live plants may make the typical values of your fishless cycling testing be somewhat off, but again, maybe not as the article was written based on tanks cycled with plants.
Note that algae growth during fishless cycling is not a given and may indeed only happen to a smaller subset of people, its hard to tell.
My hunch currently is that the Pros outweigh the Cons.
~~waterdrop~~
ps. as always, it helps to watch for advice from other members - I'm mostly a talkative beginner myself!
pps. (edit) You might want to be careful about trying to give the plants "just enough light" and not too much, too much promotes algae (algae is a complicated topic actually)
It is OK to fishless cycle in a planted tank right? Thanx so much for your help. I just don't want to waste a lot of time and money only to end up killing my plants...
