My Vanilla planifolia is wrapped around a bamboo steak, just sitting on top of some dirt. At first, I too tried to plant it in the dirt. I ended up with the same result as you. At that point, I cut off all the mush (with sterilized shears), and just left it sitting atop the dirt. After a month, or so, I noticed a new vine shooting up from the top, and a small one from the bottom, also. Your peice of vine probably won't root, it will send out new vines that root for it. Just sitting on top of the moist soil seems to create enough humidity to make it grow. At this point, if it wants to send roots into the soil, it will do so.....but they will be better adapted to it.
