I have a friend in the Fort Worth area who is a superb gardener. She's always researching ways to have healthier soil and stronger plants. We've had many a conversation about the use of compost. She feels that it should be incorporated into the top three inches of so of the soil to make the best use in feeding plants organicallybecause the plants feed mostly in those three inches.
I've read somewhere that double digging is the best way to prepare a new garden, adding compost in as we turn that soil. My friend is trying to persuade me not to disturb the soil, but to add compost on top.
She has also taught me about corn gluten meal, and alfalfa.
It seems that if you put alfalfa on your iris in the fall you'll have huge numbers of blooms in the spring. You can use pellets, meal, or hay to achieve this. I'm going to try it. I'll let you know in the spring how it turned out.
If you've tried this, I'd like to hear from you.