This old Victoria, BC house we purchased has a garden in need of rehab and I've been slowly adding new plants and mulch. There are a quite a number of old irises of which I edited out a few last year because they seemed over crowed. I noticed this year that I only had about 8 blooming stems out of about 60 plants. Do irises eventually stop producing blooms? I'm wondering if it could it be because they have gradually become more shaded from an overgrown tree, but others in the sun also did not flower. I rather like their foliage, and I hate to throw plants out needlessly, but I could use the space in the garden.
In order to bloom well Irises need to have at least a half day of sun and rhizomes half-exposed. Yours seem to have them entirely covered with soil and mulch.
That isn't the best photo. The rhizomes are mostly exposed, but the tree they are growing under has grown quite large and there is not much light so you are right about that.
When overcrowded irises do not flower so well, but simply thinning out is not the best way to deal with it. They need to be dug up, divided and replanted every few years. Replant the strongest rhizomes for each variety, and amend the soil with manure, compost etc for best results.
