Your iris will be happy in the ground for a number of years, but after a while you may find they are not flowering as well, so it's time to lift and divide the rhizomes. Or perhaps, as explained above, they are not in the best spot, and you have your eye on somewhere more suited.

The best time to lift iris is immediately following flowering, or in late autumn. Lifting in mid winter will not give your iris time to establish before blooming in the spring, and what flowers that do bloom will be small and late. Moving during summer is okay, but iris are not growing much during this time and you must be careful to not over water as you will cause rotting of the rhizome.