My iris have performed well for years. Then they stopped blooming/ I divided them and they haven't bloomed since. It's been three years now. I started adding composted horse manure in my gardens two years ago. Could this be the problem?
What Will Cause Bearded Irises to Stop Booming?
Certified GKH Gardening Expert
The most common reason for irises failing to bloom is overcrowding. Dividing and transplanting them usually helps, but since this has not helped wtih yours, there may be other factors contributing to the lack of blooming.
Your soil may have an issue. Use a fertilizer higher in phosphorus or even a phosphorus only amendment, like bone meal, to get them to bloom. Since horse manure is high in nitrogen, it has likely thrown of the nutrient balance of your soil. This article will help you: https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/phosphorus-plant-growth.htm
Failure to bloom can also be attributed to poor pollination. Try to entice pollinators (bees, butterflies, etc.) to the area with brightly colored flowers.