Wetting depends on the comparative surface energy of the liquid and the substrate. If the substrate has a higher surface energy than the liquid, in this case water, the water will flow and "wet" the surface. If the substrate - in our case, peat - has a lower surface energy than water, the water will bead up and will not wet the surface.
There are two ways to make the water "wet" the surface. One, increase the surface energy of the substrate. In industrial processes, this is often accomplished by etching the surface using a chemical or a corona or plasma discharge. Kinda tough to do on peat. Two, reduce the surface energy of the water. This is why people add wetting agents to the water.
I can give you a perfect example to show you how to use soap to make water wet something. sprinkle a few drops of water on the surface of a freshly waxed car. The water will bead up and roll off the surface. Next, take the tiniest bit of soap and touch one of the water beads. The bead will instantly flatten and wet the surface. If you don't have a freshly waxed car, you can cut a piece out of a polypropylene milk jug and do the same test. LDP or low density polypropylene is a low surface energy plastic. Make sure the pastic is super clean.
Wetting agent for grow media? Dr. Bronners liquid soap. Reduces the surface energy of the water. Readily available, organic, effective and cheap. I like the peppermint - makes your balls minty in the morning.
