I have a Regina Iris that has been in the ground for almost 2 years. It has not bloomed as of yet. I have it in part shade/part sun. It has grown quite a bit and has spread but no blooms. I have fertilized it with Osmacote just a couple of weeks ago. It get's watered 2 x a week by sprinklers.
Why Is My Regina Iris Not Blooming?
This article contains general information on 'Regina' iris: https://www.gardeningknowhow.com/ornamental/bulbs/walking-iris/walking-iris-plants.htm
Walking iris species are generally considered quite unfussy and easy to grow. If you have a flowering plant that has healthy foliage but no flowers, there are 2 general things to look at. 1. is light - the plant often needs more light.(some sources suggest some types of regina need 6 hours of sun per day) 2. is fertilizer - the plant often has too much nitrogen and/or not enough phosphorous.
Try getting more light to the plants, either by moving them or by removing some of the shading foliage. Also, try working more phosphorous into the soil in the form of bone meal.
Watering 2X week should be sufficient, but feel the soil down around the roots a few days after watering, to make sure it's damp - reginas don't like drought.