Soil improvements for iris

I don't have soil. I have river sand, 30 ft deep, not even a pebble, sooooo easy to dig, grows things great as long as you pour the water and nutrients to it.

I recently have access to, free for the hauling, Ardmore OKla, city compost from sewer sludge and ground up tree trimmings, it is well composted, smells fine ( inspected and approved for garden use) but doesn't look at all like rich dirt yet. I can get it once a month by the dump truck load. I am sprinkling it all over my gardens, scratching it in when and where I can. ..sure hope I am doing the right thing. Anybody done this for iris ever?

Pictured is Splashacata, last year

I would just apply a little, there are some nutrients lacking in that mixture, such as garden scraps. Compost consists of alot of different things, and it should not be hot. Hot compost will kill just about anything it touches. It will fertilize but some may need to be added.