I have mature iris plants, but they won't bloom. Any ideas?
The most common reason for irises failing to bloom is overcrowding. Dividing and transplanting them usually helps. In addition, it can be attributed to poor pollination. Try to entice pollinators (bees, butterflies, etc.) to the area with brightly colored flowers. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/iris/dividing-transplanting-iris.htm
Also, use a fertilizer higher in phosphorus or even a phosphorus only amendment, like bone meal, to get them to bloom. This article will help you: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/phosphorus-plant-growth.htm