I use it......several ways, Like you read, a "sprinkling" around the plants seem to really help with bloom....I do it really early, just as new growth starts, and, for the rebloomers, another "sprinkle" just after the "spring" bloom is finished. There is a relationship between the amount of phosphate, and the amount of nitrogen ( I forget the exact ratio, but you can probably "google" to find it), so , in other words, if the right amount of nitrogen isn't present in the soil....all of the phosphate won't be available to the plant, and will just 'leach out' of the soil.
Depending on what other 'amendments" I'm adding to the soil( alfalfa pellets, for example have a nitrogen content, as does "organic' Preen, or corn gluten meal), I take plain ,old 10-10-10 fertilizer, and mix it , 50 /50, with the triple super phosphate, which is 0-48-0(at least the "brand" I use...that results in a final "mix" of 5-27-5, which is just about perfect for bearded iris......but, remember....if you are adding other products that have a nitrogen content, you have to be carful not to end up TOO high in nitrogen. I would recommend that before adding ANYTHING to the soil, in the way of fertilizer amendments, that a person has a soil test done, to see just what your soil is lacking (if anything), as well as to get the 'ph" tested....the ph has to be "right", or the plants can't use the fertilizer.
