Tulips need to have yellowing or dying foliage and iris are best to move after they have bloomed.

I'm no expert, but I think tulips can be dug and moved as soon as the foliage is dying back. As for iris,I've been told that they should not be disturbed until August, when they should be cut down to about 8 inches and they can be dug and moved. There is an iris forum. Why not get it straight from the horse's mouth? Probably many of the people on that forum would be expert iris growers. Carmellia

Thirty days or so after irises bloom they start to put out side increases which are the rhizomes that will mature and bloom for the following year. This years blooming rhizomes will not bloom again- just act as "mothers" that produce the babies and it's roots will feed and water the new little ones until they form roots of their own. Dig now and the iris might not have the energy to produce the increases needed for next year. But- they aren't as fussy as this rule of thumb sounds. I dug a bunch last year right after bloom and threw them in the woods where they are happily growing this year simply sitting on top of the soil. Go figure! I kill more plants with fussing and kindness than I do neglect.

Nettie - I was interested to read your reply. Does that mean that the rhizomes that are not blooming this year will not bloom again - that they are the "mothers" from past years? What I am wondering is should I discard the non-bloomers? Thanks for the info. You sound like a true iris devotee. Carmellia

Not necessarily Carmellia; they may be immature rhizomes that take more than a year to mature and bloom or they may be an unhappy rhizome that is not getting enough sunlight or is in an overcrowded clump. The mother rhizomes will usually shrivel up and die out naturally- no need to remove them.