Not too deep! Iris plants like to grow near the surface, so plant your iris bulbs 3 to 4 inches deep. Dig a hole that is about twice the size of the bulb.

more at link:
http://www.life123.com/home-garden/flower-guides/flowering-bulbs/iris-bulbs.shtml

Why did they bloom the 1st year? Bulbs don't sink deeper each year, do they? I have other bulbs that were planted at the same time and they've come up each year.

with mulch, leaves, soil. Each year you need to scrape them gently so that the rhizome surface is exposed. If you do that, and they get full sun, they should bloom again.

I have other iris that are rhizomes.

so perhaps insufficient sun, or some fertility (nutritional balance) issue? I've not planted them before.

then nothing. Sounds like I need to dig them up and replant them. Do I dig them up now or wait til the green stuff dies? Does it make a difference? I'll replant them in the fall.

then re-set them. They are really nice - I've seen them as cut flowers. good luck!

Too much nitrogen makes leaves but no flowers.

Thanks!

Do the rhizomes break through the earth? They like to lump up on top of the earth. Cut them back almost to the ground, fertilize with good like bone meal. If they are too crowded, they won't bloom either.