One way is to stick a toothpick through them near the bottom of the stalk (~1" from the bottom, depending on frag size). Then use a rubberband to loop around a rock and loop it over the ends of the toothpick. That will snug the toothpick/frag down to the rock and it will attach in a few days. Don't get it too tight, or it will cut through the stalk. Too loose and the frag will not stick very well. Another way is to wedge it between two small rocks and let it attach by itself. HTH