Alternanthera reineckii & stem rot under gravel?

[motifone]

My Alternanthera reineckii needing a pruning. I cut about a couple inches off the bottom, plucked off some of the lower leaves, and replanted the stems in individual holes maybe a node or two deep. The nodes above the gravel have white roots, but none quite long enough yet to reach the gravel. A few of the stems have since floated out from the gravel and I've noticed that most of the buried stem has rotted or is in the process of turning to mush.
Am I not burying the stem deep enough? My guess is that a little rot is normal, but by the time the roots get hold, that keeps the stem anchored & fed, and the rot stops? Am I on the right track? Maybe I need to bury at least 2-3 nodes so the roots can catch up?
Any thoughts?
Oh, I use 100% Flourite.

steve

[Anthony]

I have noticed this also with alternanthera, as well as l. gladulosa.

[Urkevitz]

Alternanthera is extremely bouyant, especially when the plant gets larger. When I was growing it I would bury it as deep as possible, leaving the leaves on the stem to help it stay anchored

[Momotaro]

Agreed.

Plant it as deeply as you can and don't worry about it. The plant will eventually send off roots and anchor itself in your substrate. The plant manages to do that in most aquariums and in nature, so you'll be fine!

Mike