With a rhizomatous iris like a bearded iris or beardless iris, the rhizome still needs to be partially exposed. What zone do you live in? Are the iris leaves green year round?
You can dig up one of the iris to tell if it is rhizomatous or bulbous. You can do this without damaging the plant. Go past the end of the row about 3 inches and with your spade angled toward the iris go down about 8 inches and pop the iris up. Brush the dirt away and look at the roots. Are they attached to something that looks like a bulb or something more tuberous?

Strangely enough, there was a board there completely shading them for a few months until I remembered to move it. That one had grown to almost five inches! But that was almost two years ago now.

There are four or five in a row there, but I don’t know if they’re rhizomatous or bulbous… is there a way to tell without damaging them?