I've gotten a lot of good information from this forum over the past year or so that I've re-entered the hobby. Since this has been my first venture into live plants it's been particularly helpful.
I've run across a trick, and wanted to give back a bit by sharing it. I haven't seen this anywhere, so forgive me if I'm putting up something that's already well known to everyone, if that's the case, I've just managed to totally miss it. (shrug)
Background: I've been planting Val of various types, and had trouble keeping some of the plants in the substrate due to their roots being too short or to few to get a good hold (a circumstance which the MTS really are not helpful with).
I thought about this for quite a while and finally had a brainwave that has panned out. After reading here about tying plants to rocks/driftwood/etc. with cotton thread, and how rots away slowly enough that the plants can anchor well, but fast enough that it's not a permanent decoration, I finally realized I could use a similar approach to add artificial "roots" to my root-challenged vals plants.
The Trick: The basic idea is to cut a rectangle of cotton gauze and wrap it around the roots, then plant that into the substrate. The gauze substitutes for the roots, but allows new ones to grow out through it. As an extra benefit, for plants like vals, it can be a visual aid for getting the planting depth right: wrap it just below the crown and plant it deep enough that you can't see the gauze, and you're good to go.
Details: First, you have to make sure you get cotton gauze that doesn't have any kind of treatment on it (antibiotics/lotion/whatever they put on the stuff) which would probably be ... undesirable for obvious reasons.
Second, unfold the gauze completely so that you have a single layer of the stuff. At this point the threads will shift around a lot if it's handled too roughly, so a bit of delicacy is in order.
Next just cut a rectangle of gauze with a pair of nice, sharp scissors. Use the size that seems best for what you're planting. It seems to work best if it wraps around at least twice, and you should make a long enough "root" for your planting intentions. The water in the real roots will kind of temporarily stick the gauze to the plant, making wrapping pretty easy. I've found that giving the "roots" a light twist will make them stay rolled a bit better.
Finally, grab the end with your planting instrument of choice and shove it down into the substrate. All done. The weight of the substrate keeps it wrapped around the plant snugly, but not tight enough to cause the plant any distress.
It also occurs to me that this might also be a way to grant some protection during planting to plants with particularly delicate roots. As mentioned above, I've really only used this for vals, but I don't see why it couldn't work for other plants.
I hope that's helpful to someone.