I don’t know why every time I plant stem plants into the gravel the base of the stems almost always wind up rotting. It happened to me with the wisteria I have so I just gave up on it and floated it (its doing great now as a floater BTW). I got some ludwigia a few weeks ago and planted it on the substrate and like the wisteria it’s starting to rot at the base of the stems. I add root tabs and liquid fertilizer. Really don’t want to float this plant as I love the way they look when clumped together like a bush.