By Bonnie L. Grant Irises are one of the easiest flowers to grow. They stem from rhizomes, which quickly multiply over the years, producing bigger, wider stands of these appealing blooms. When you notice iris plants not flowering, the cause can stem from a variety of issues including weather, soil fertility, overcrowding, unhealthy rhizomes, insect or disease attack, planting depth and even site conditions. If you are wondering, “why are my irises not blooming,” take a good luck at these issues. Usually, we will find iris plants not flowering due to one of these easily corrected conditions. Why are My Irises Not Blooming? Bearded or Asian, classic or designer, irises are a pleasure to have in the garden. They provide a long term display of tall, glorious sword-like leaves and boldly featured blooms. Most irises have a wide hardiness range from United States Department of Agriculture zone 4 to 9.