Did you just stick the stem into the box with some filter floss?
I did before i found out the roots love filter floss. It makes it a pain when cleaning because you have to basically clip off all the roots to throw out the filter floss. So, now I just use the regular sponge blocks and that's it. Just stick the stems down around the sides of the sponge and they stay put.
What are the potted plants at the back sitting on or are the clipped somehow to the back side of the tank?
They're in 9 inch plastic planter pots and on top of some 3 inch Styrofoam blocks. I had a little room left on the table behind my tank so that's why I started putting Low Light terrestrial plants back there. no clips or anything, just on the extra table space available.