Made laundry soap -- 70% coconut oil, 30% lard, 0% superfat -- yesterday and got it processed into a powder today with washing soda and generic oxiclean. The trick is to get the soap grated and broken down to powder while it is still fresh. Once the soap dries, even for a few days, it won't powder well.
I'm getting away from adding baking soda and borax that you usually see in most laundry soap mix recipes. Here's my latest recipe for laundry soap mix:
80 oz grated soap with high percentage of coconut oil
110 oz (2 each 55 ounce boxes) washing soda
80 oz oxiclean-type oxygen bleach powder
All weights are approximate. Grate the soap by hand or with a food processor. As you work, spread the grated soap in shallow pans to cool. Using a food processor fitted with a blade, add a large handful of grated soap and about the same amount of powder (washing soda or oxiclean) to the processor bowl. Don't overload the bowl for best results. Process about 30 seconds to a fine powder, but watch carefully that the mix gets finer and finer -- you do not want it to do the opposite and start to clump up, and that can happen really quickly. If at any time you do see clumping, stop immediately and add another handful of powder. Resume processing. The point here is to keep the soap cool and covered with dry powder, so the soap continues to break down into finer and finer bits, rather than clump up. Spread the powdered mix out into shallow pans to cool. Evaluate the powdered mix. If you want a finer powder yet, process the cooled powder another time and see if you can break the powder down even more. Depending on the soap, you may be able to get it very fine, but sometimes that just doesn't happen. When you're satisfied, pack the cooled powder into an airtight container and store in a cool, dry place.
I also made a gardener's soap. I used a tried and true bath soap recipe and made an uncolored batter. When it was at thin trace, I separated out about 1/3 of the batter and added finely ground coffee to that to make a scrubby brown batter. This batter went into the bottom of a slab mold. I added a dusting of cocoa to define the boundary with a brown-black pencil line. Then the plain batter went on top.