If the garden was neglected, then it is probable that the iris have not been divided in a while. Iris like to be divided every 3-5 years. Sometimes it is harder to tell when they are crowded because the rhizomes can grow on top of each other. Also, I'm not sure that 3-4 hours really is enough. I would try dividing them in a month or 2 (I divide in July), & try them where they can get a bit more sun. If they are bearded iris, but sure not to plant them too deep. I leave the top of the rhizome above the soil. Toss the old part of the rhizome that has already bloomed & plant the healthy new rhizomes.

thanks much, ngraham! you answered all my questions so perfectly. i took a look at them and now i think they need both division and transplanting! i still don't quite know how to tell what is the part of the rhizome that is already done and what is not, but i will see if i can find that out with some research on this forum. many thanks again.

i still don't quite know how to tell what is the part of the rhizome that is already done and what is not,
Any rhizome that has bloomed will be a 'mother' rhizome, and it will not bloom again, but it will grow 'daughters' off to the sides of it, that will be 'blooming mothers' in a year or two, if all goes well. It should be easy to see the 'mothers' from this season, (can see where bloom stalk was even if bkoken off) as well as from past seasons.

Also...any rhizomes that are shriveled up, or flat, or that have just dried out roots attached, or just have holes in the bottom of them where roots once grew should be pitched. These are all old mothers, or else just rhizomes that have died off due to overcrowding.

You might want to check out the FAQ here (link at the top of the first page here) about irises not blooming and also digging and dividing and resetting your iris.

Sue