Exposed iris bulbs

Exposed iris bulbs

I have a quick couple of questions about irises. The ones I have were planted when my parents lived in the house I currently live in, which means anywhere from 15-20 years ago. They've been trucking along with little human interference since planted. The other day, I was out trimming the dead stalks and cleaning up some old leaves that had collected around their base. I discovered that, under the dead leaves, the iris roots/bulbs/thingies are basically just sitting on the ground, not covered by dirt at all. Please keep in mind that the extent of my iris knowledge is that they're pretty, okay? 1) Would it be better to get some gardening soil and cover the roots without disturbing them, or should I move them, dig a hole, and bury them? (Or are they supposed to sit on top of the ground? I was a kid when they were planted, but I don't remember them being exposed like that.) 2) Somewhere in the back of my mind is the notion of thinning or splitting up iris bulbs so they don't choke each other out. Is there any truth to that notion? If so, what should I be doing and when?
KAWAII ROOM MAKEOVER~

KAWAII ROOM MAKEOVER~

Room Spam!

Room Spam!

1/3 of an acre covered in blackberries is becoming

1/3 of an acre covered in blackberries is becoming

Apartment

Apartment

We re-did my room and replaced the floors and painted the walls

We re-did my room and replaced the floors and painted the walls

Mid Century Modern Picsplosion

Mid Century Modern Picsplosion