What's all the perlite for? It serves a different purpose than mulch. Mulch is used as a top dressing to improve water retention and prevent the growth of weeds. Perlite is used for aeration and to prevent soil compaction. I used to add extra perlite to peat based mixes like pro-mix, but I found it to be an added expense with little return. After a few good waterings a good portion of it ends up floating to the top anyway. If you are making your own soil it might be a good idea to add some, but imo it isn't worth adding if your mix already comes with some. A nice thick layer of mulch, on the other hand, will help retain water by lowering evaporation. If you are looking for added water retention, vermiculite is what you are after.
