A gardener in my neighborhood group asked for advice on why her bearded iris bed wasn’t blooming. It had bloomed in the past, but now there were only foot-high leaves, with no flowering stalks.
I answered her post with a list of conditions that could be responsible. Maybe you’ll find it helpful, too.
1. There’s not enough sunlight. When bearded irises are planted in the shade, they will often produce only leaves. Make sure they get 6-8 hours of sunlight per day (more is better). In some warmer climates bearded iris falters during extremely hot weather, but in southern New England, that shouldn’t be a problem.
2. The rhizomes are lousy. Bearded iris rizomes should be about a little fatter than your thumb, and firm (not mushy). If they’re crowded, dig up the bed, separate the good rhizomes from the mushy ones, and replant. But don’t do it in June. I would wait until early August (6-8 weeks after their normal bloom time). When you dig up the irises, use a spading fork instead of a shovel. You don’t want to cut the rhizomes.
Bearded irises are pretty tough plants, but don't overlook their basic needs -- loose soil and full sunlight for starters.
3. The rhizomes might be planted too shallow or too deep. They should be just beneath the surface, so you can sometimes see the tops exposed in a few places. But you don’t want all the rhizomes exposed throughout the bed. If they’re planted too shallow, the fix is easy. Just cover with an inch of compost or well-rotted wood chips. Don’t pile on a thick bed of mulch, as it can cause rhizomes to rot — especially if soil doesn’t drain or the site doesn’t get enough sunlight. (Which brings us to Reason No. 4.)
4. Soil doesn’t drain well. Iris likes loose, well-drained soil. So if soil is compacted, water doesn’t drain, rhizomes can rot, and plants don’t perform as well. If they’ve never bloomed, maybe the soil isn’t friable enough. Add compost or leaf mulch and mix it in.
5. Fertilizer and/or pH is wrong. Bearded iris are not fussy, but if you don’t have phosphorous in the soil, and it’s too acidic (plus you have varying degrees of the previous four conditions), your iris bed could be lacking vigor. Iris like the same soil as most vegetables — slightly acidic, but near neutral (about 6.8 on the pH scale). You might want to test the soil if you’ve never done it. Unlike lawn grasses, bearded irises don’t need huge amounts of nitrogen. Compost from manure will probably have enough phosphorous, but you could add a little 5-10-5 (all purpose fertilizer) with twice as much P as N and K.
6. For more information, check out the American Iris Society web page. and the second is my blog: Iris Society: https://www.irises.org/About_Irises/Cultural%20Information/Grow_Bearded.html
If you like Bearded Iris, you'll love Siberian and Japanese Iris. Siberian Iris forms massive clumps that explode into bloom around the first of June. They also require very little care if soil and sun conditions are right.
If you like bearded irises, you should love Siberian and Japanese Iris. Siberian iris plants grow into a magnificent clump that blooms in early June. Japanese irises are my personal favorite, growing into thick clumps like Siberians. But Japanese Iris (Iris ensenata) are have larger, showier flowers. And the plants can live in standing water, which makes them excellent candidates for growing inside pots along the perimeter of your koi pond.
Japanese Iris can be planted in large black pots and placed along the perimeter of a koi pond. The foliage looks attractive enough, but the flowers are stunning in late June.