A general rule is to divide every 3 years. This can vary with different cultivars and different growing conditions.

Ideally the mother rhizome that is blooming puts out babies to the side and she dries up. So yes, you can have the same iris forever. But . . . . . . . . rhizomes can rot, babies can fail to appear, extreme drought, etc.

Do not plant deeper. Since you had a glorious display last year (the 3rd year) your iris must be happy water-wise. Are you sure you're just not seeing old spent rhizomes? Sow bugs are little scavengers. They love my pansy buds. Some years worse than others.

Sorry I can't shed more light on what you have. If the fan with blooming stalk is coming directly from a wizened, shriveled rhizome I would mark that rhizome and keep watching it thru the summer to see if it produces babies. Maybe you could capture a picture of it?

The real danger sign is when the rhizome begins to get mushy. Then it's imperative to dig, cut away rot, soak in 10% bleach solution for 30 min., dry thoroughy, and replant in well-drained soil, which is allowed to dry out between soakings.

carol in our climate i think dividing every year is best, at most 2. the gorgeous displays you see at napa and superstition are because they use new nutrient rich soil every summer, along with oregons better display beds. i think your soil is depleted, plus we had the direst winter, following one of the wettest prior! in other words everything must have leached out the prior year and this winter there was barley enough water to keep them alive, much less flourish! if you enhanced your soil i am guessing they never had enough roots to make it thru the nearly bone dry winter, i have the same thing happening in my garden too. this summer is a massive do over with tons of new compost and gobs of water to get them happy again!
ps did i see you at napa on sunday?

Thank you both for the specific and sensible advice. I have noticed, jain, that a neighbor waters her irises (overhead sprinklers) 2-3x a week even now, and her irises get afternoon shade, which mine don't. I will definitely give the beds much attention this summer. Iris gal, all the rhizomes I kept this last season were the babies, but they quickly started to resemble their shrivelled parents. I googled images of iris borer damage and rot and am very relieved there's no resemblance between those pictures and my rhizomes. I wonder if they are sunburned. I plant them with tops just above the soil, but the soil settled and some are 2/3 exposed now.

It's interesting that the bud-covered stocks that DO bloom push the open flowers into spent, closed, slimy fists to make room for next bud down on the stem so quickly I feel like I'm deadheading daylilies. They're still the most breath-takingly beautiful flower I know, and I won't give up on them.

My husband and I drove up to Napa Country Iris Gardens on Saturday. Is that the place you're referring to, jain?
Happy May!
C

I doubt upper exposure of the rhizome is the problem. Rhizomes like to sunbathe in our zone. 1/2 exposed is the usual planting depth.

"... push the open flowers into spent, closed, slimy fists to make room for next bud..."

Don't understand this. Old blooms can be rather slimy.

Here in south eastern Washington we had a wet winter last year and nothing bloomed. The year before that is when I planted and one bloomed. This year the one the bloomed the first year has a pod, but it looks dried on top of the green bottom (it is brown) and I am keeping an eye on it to see if it blooms. This is not unussual my friend the hybridizer has 1/2 an acre of irises and only 1/4 bloomed and some of them were damaged. His Lillies suffered stunting and similar damage. Just keep an eye on them and prey that they bloom.