Yamagoke - Dried Japanese Mountain Moss for Surface Root Protection
Yamagoke is the go-to for a surface covering after repotting and for shallow-rooted species like azaleas, crepe myrtle, etc. It is leaps and bounds better than sphagnum moss. It readily re-wets, it is a naturally smaller size, permitting it to nest better to resist being removed during watering, and in many cases "come back to life" during the growing season. Being a true moss, it will not invade your soil with roots, should it spring back to life, but instead give you a nice, green carpet over your soil.
Each brick is extremely densely packed and will cover a great number of trees. If you wet too much, simply let it dry out and then add it back to the package. There is literally no waste.