(Image credit: Shutterstock) There's something quietly defeating about walking past your garden bed in spring, seeing a flush of green leaves reaching upward, and waiting for flowers that never come. Irises are dramatic, gorgeous bloomers, and when they go silent, it's worth figuring out why. Almost without exception, the culprit isn't disease or pests. It's a shift in growing conditions — something that's crept up gradually and can, with a little patience, be undone. Just be prepared: irises work on their own timeline. Article continues below 1. They've outgrown each other Irises are sociable plants, until they're not. Over time, the rhizomes underground multiply and crowd together until they're competing for every bit of nutrients and space. The foliage keeps going, but the flowers quietly disappear. Every three to four years, dig the whole clump up after blooming finishes in late summer.…