There is disagreement on this issue. Are you going to use it as a mulch or dig it into the soil?

To be safe, I would keep it away from the top of the rhizomes. Irises do not require much nitrogen, if that helps.

I use it too, but we should be aware that it contains high levels of salts from the urine, and those salts build up in our soil. I have been getting horse manure from a woman who cleans her stall every day, so there's no urine in the manure, then I compost it.

I am going to work it into the soil & make a nice mound for better drainage. We have heavy clay & the steer manure does a great job making it loose & drain well. This spot will get hit by the lawn sprinkler often in the summer, so it will be on the wet side. I need it to drain & dry well. I dont plan on using any mulch of any kind. I could probably get horse manure, but it would not be composted.

I usually use around 50/50 50% dirt & 50% composted manure.

Are my iris going to rot if I use it?

I always lay my hand on a bag of manure to feel how much heat is being emitted. If it feels warm (out of the sun of course) I let it age in tha bag a couple of months - until it is cool to the touch.

I have *adobe* soil and I find 1-inch of 'cool' manure dug into the top 6 inches of soil each year works well. 2-inches when I'm digging deeper. More than that and perrenials and annuals don't thrive. I suspect the salt content as well as the 'rawness'. My favorite amendment for clay soils is nitrogen reinforced redwood sawdust. It breaks down so slowly that friability is maintained longer, as well as combatting the akalinity of our soil.

My best iris bed was created in the spring with 1-2 inches of cold manure, a sprinkle of bonemeal & a sprinkle of superphosphate dug down about 16 inches. New rhizomes planted late summer.

I wont be planting till later this summer/fall & the bags of manure were bought last spring/summer so they should be well composted.
Nitrogen reinforced redwood sawdust sounds interesting, I wonder if plain redwood sawdust would be ok?
The spot where the iris are going currently have 3 large redwood trees that will be cut down, so I should have lots of sawdust & chips.

You'll need nitrogen, then, because plain wood chips or sawdust take up nitrogen in the decomposition process and rob the soil of it. You can buy cheap ammonium phosphate for that, or compost the sawdust first with manure.

Hey Halibut ~~

Nitrogen Reinforced sawdust. Very Very Important!!!

As Hosenemesis says, the process of decompsition uses up the available nitrogen. Nitrogen is one of those elements which moves freely thru soil --- it doesn't attach.

The Rodale Book of Composting is full of excellent info.

Most people report poorer performance of plants near root systems of trees. I've not gardened near redwoods but I have very depleted soil from a 30 yr. old purple plum tree with ivy growing thru it --- removed 3 years ago. No wonder what I put in has had a failure to thrive!

I dont think I have enough time to compost my sawdust so I dont think I will be using it, or not too much of it.
Nothing close to the redwoods grows good, it all grows very poor! I have no other space for the iris, I have to do all I can to improve the soil & hope for the best.