This is what I tell gardeners about the use of alfalfa:
For long term affect for hostas, especially, and daylilies, soak alfalfa overnight, and put four cups of the mixture in each hole where you will plant.
The alfalfa cubes are cheaper and will be more slow release, feeding hostas up to four years. I am just recently using for daylilies the same way and I do not have much data on the duration of feeding.
Making sure that the mixture is very watery is very important, and make sure to water it daily for the next week or so.
For established plants, especially hostas, use this mixture as a side dressing. And again, water daily.