Irises shouldn't fall over after being transplanted as long as you cut the foliage back to 6-8", If they have no roots at all, you may need to stake them until they grow new ones, but typically the trader will have left enough root on to hold the plant upright with trimmed leaves.

Assuming these are bearded irises, they prefer very well-drained, friable soil (raised beds are ideal) in full sun. They are tolerant of a fairly wide range of soil pH, from moderately acidic to moderately alkaline. If your soil is virgin to irises, chances are it doesn't need much in the way of fertilizer to keep them happy. It wouldn't hurt to have your soil analyzed through your local county extension service, though, to see exactly where your soil stands nutritionally. The soil test will tell you exactly what, if anything, you need to add for optimal plant performance.

Avoid use of high-nitrogen fertilizers or amendments. High nitrogen can promote rapid, soft growth that is particularly susceptible to bacterial soft rot. It also promotes leaf growth at the expense of bloom.

Plant beardeds so the tops of the rhizomes are level with or slightly below the soil surface.

Be very careful not to overwater bearded irises. One deep soaking after planting should be all they need to get going unless you live in a very arid or drought-prone area. Overwatering is another almost surefire way of promoting rot in beardeds. It's also best when watering to use soaker hoses rather than overhead watering.

Early next spring just as the irises are starting to grow, you may want to consider applying Merit, since you do live in iris borer territory.

Happy irising,

Laurie

I'm in Zone 5, but in Wisconsin. I have heavy clay which the rhizomes seem to love. I plant them so they are just at soil level and water them well because then the clay forms tightly around them and holds them fast.

My biggest problem with freshly planted Iris is squirrels re-arranging them. If they pull them out I just place them where they came from and step on the rhizome to adhere it more firmly to the soil. Seems to work - at least in my neck of the woods.