Planting the cutting of stem plants

[Maggie]

I think this is a lidwigia repens. It grew to within an inch of the top and then started bending to stay submerged, so I trimmed it. There's new growth on the remaining piece, and several roots have started growing all along the length of the cut piece that's been floating - it's really cool! If I leave it floating, will the roots get long and flowing? If I plant it, will the "extra" roots stay, or will they dissolve once the substrate roots take off?  This is one of my few very successful plants so I'm having fun watching it thrive. 

[Celly Rasbora]

Nice. Letting it float should grow some roots. I can't seem to grow it myself.

[Koi]

Once you see aerial roots you can begin planting the tops you cut off. Most times you can even cut the tops of ludwigia with out seeing roots and it will grow. Waiting for the aerial roots to develop just makes the process that much quicker when planting. Floating the plants at the surface of the water is a good trick if you need to force something to grow roots.

I suppose you could leave the stem floating if you'd like, the aerial roots will grow longer and you might even see multiple shoots of new growth horizontally across the entire stem. But if your goal is to plant it, the stem is ready to go. If you really enjoy the process of propagating, you can pluck off a few of the lower leaves before planting. It is rather pedantic and not necessary but I do enjoying physically inspecting the health of my plants. 

Edited March 11, 2021 by Koi