I use it on my irises and bulbs.
I give my irises a tablespoon each mixed into the soil when I plant them out and then I give them a light sprinkle in spring, when they put up new fans and again after they are done blooming.
I'm sure there are other ways to do it - especially if you are in a different zone, but this works very well for me. Mind you, my season is short and I have only ever had 're-bloom' on newly planted irises, which have been a little confused.
