I have a solution to the problem of securing plants in plastic pots. I
seem to need this a lot - rootless divisions, topheavy plants.I don't
like to pack the mix tightly, so a stake down through it won't help. So,
for bulbos (which can be shaped like a roller coaster), any catts,
milts, brassias, tall dens, etc, I find rhizome clips don't work well
with plastic pots. I use an old soldering iron (alternately a long
rhizome clip laid over a stove burner on high for a short while,
carefully handled with a potholder) to burn holes in the sides of the
pot opposite each other just a little below the level of the rhizome.
Then I insert a bamboo stake (from the grocery for shishkabobs) which
should be just snug enough down on the plant to hold it firmly. I leave
about 1/8-1/4" of it sticking out either side and clip off the excess
with wire snips. Works great, is inexpensive and so adaptable to
different plants and pots.