||Retaining walls need more than blocks to be constructed properly. Along with the blocks, one needs caps, stone, draintile, glue and larger retaining walls will need geogrid.
This page lists resources for the miscellaneous materials needed. See the material checklist for the do-it-yourselfer.
Draintile is used near the base course and is daylighted through the retaining wall to remove any excess water. Black four inch corrugated plastic soil drain pipe is normally used.
Glue is simply used to adhere the caps to the top course of blocks. One of the recommended brands is Liquid Nails LN-901 Heavy Duty Construction Adhesive.