The reason for layering can often be to increase the number of plants, but for me it is to stop the plants outgrowing the terrarium where they live, and having spare plants as a result is a bonus which I can then swap for other specimens. Choose the stem you want to layer. Cut off a leaf at the point where you want to do a layer, as in this photo:
Nepenthes air layering 01 by gardenofeden67, on Flickr
Then make an angled cut upwards through where the leaf attached to the stem using a clean sharp knife, as so:
Nepenthes air layering 02 by gardenofeden67, on Flickr
Press a few stems of Sphagnum into the cut. This is to keep the cut open and stop it from healing up. I have tried doing notches before, but find this "wedged cut" works much better. Some people like to use hormone rooting powder, although it never seems to work for me. There has been a recent suggestion that rooting powder may work better on layerings done towards the top of vine because of the particular hormone balance near the shoot tips... I tend to do mine towards the bottom of the vine, which may explain why hormones do not help:
Nepenthes air layering 03 by gardenofeden67, on Flickr
Next wrap some damp Sphagnum moss around the cut. You do not need very much, a ping-pong ball size is as much as you will ever need and usually much less than this. Wrap a piece of clear plastic (e.g. cling film) around this Sphagnum, and secure top and bottom with ties. Leave the top tie slightly loose to allow water in, you do not want the moss to dry out. You may need to water the moss occasionally with a syringe or pipette to keep it damp:
Nepenthes air layering 04) by gardenofeden67, on Flickr
Several weeks later, you may see roots growing under the plastic, Nepenthes roots are black. In this picture you can see Nepenthes roots growing in the crease of the plastic at the bottom of the wrapping. When you see the roots, you know the layering has rooted and you can cut it off:
Nepenthes air layering 05 by gardenofeden67, on Flickr
And here is the finished article with roots sprouting ready to be potted up. The stem has already been cut.:
Nepenthes air layering 06 by gardenofeden67, on Flickr
Any handy hints or useful pearls of wisdom please do share...
Edited by gardenofeden, 04 March 2012 - 12:54 PM.