The improved drainage was a good idea, but if you filled those top few inches with nothing but coarse sand, you created an almost sterile and void environment for the irises in terms of essential nutrients. Rainfall probably leaches nitrogen out of the sand almost immediately, and bearded irises do need some nitrogen. Perhaps a balanced foliar feed several times a year would help keep the plants adequately fed.

I don't know about turkey manure, but I wouldn't recommend any manure that isn't very well composted. You might be better off removing 1/2-3/4 of the sand from that bed and mixing the remaining sand with some rich topsoil. You'd still have excellent drainage by virtue of the raised bed, but the soil would be more nutrient-retentive for the irises.

Laurie

If you raised the soil level, the irises may be too deep in the ground now, too.

Rather than just piling it on your old soil you may want to dig it into your old soil. Thus you should improve drainage and soil fertility. You didn't mention ever dividing your iris. If you haven't, my own rule of thumb is a handwidth between all fans. When they get more crowed than that the whole beds health seems to suffer.

gmason, I read with a great deal of interest your comment re. spacing and thinning. Wouldn't this mean you have to thin almost yearly? All of my fans withing the clumps are much closer together than a handwidth.

More and more in urban gardens, the luxury of rotating beds, resting soil, building a new bed is gone as building lots get smaller. The temptation is to plant too many iris in too little space. The spacing I mentioned is minimum spacing for good health.

gldno1, I believe the difference may be in rhizome size between those grown in MO and those grown in gmason's garden which, if I'm remembering correctly, is located somewhere on the West Coast in "Iris Heaven". If gmason's rhizomes grow to the typically gargantuan size of many of the West Coast iris growers, then the fans in his clumps will naturally be spaced further apart. Midwestern rhizomes, however, typically mature at much smaller sizes, so the fans in a clump will be naturally spaced more closely together.

Laurie

What I have heard is that a fertilizer with a slightly lower first number is best - so something like 6-10-10. This helps prevent too much vegetative growth and promotes bloom.

Poultry manure is very hot. Make sure it's well aged or it will burn. I've even seen it eat through metal sheds.

Add a little lime, now or late fall. Takes time to work. Don't lime beardless iris, can kill or seriously set them back. Unless your sitting on one of the rare limestone deposits on North americas east coast a little lime won't hurt, probably will help and is real cheap. Bearded iris like calcium. Little bit of epsom salts sprinkled in now and then too.
Because the east coast soils and bedrock are much older than the west coast a lot of the easily solubable nutrients have gone too deep for most plants to reach. Calcium and magnesium being the big ones.

Nitrogen grows foliage, phosphorus grows blooms.
Iris actually like the soil a little on the poor side.

I'd mix the sand and soil up too. After bloom season would be best. Too much disturbance and they may abort blooms. Probably won't bother the plants much but inorder to gain strength from a transplant a lot of plants won't bother using strength flowering.

I don't use much in the way of commercial fertilizer but I have spread an all purpose 10-10-10 after bloom with no problem. Light feeding and once or twice after bloom. Plenty to hold them until spring. You really don't want to kick them into high gear while the soil is still real wet or too late in the fall either. Honestly they are better off a little hungry.