Inadequate sunshine, insufficient watering and overcrowding can cause a bearded iris to lack flowers. In addition, being planted too deep or getting too much nitrogen will prevent flower growth.
Most bearded irises prefer full sun. Tree branches and other surrounding vegetation can shade the iris. Cut back foliage to allow light to penetrate to the flower. Some varieties do well with at least half a day of sunshine.
Though these plants are considered to be drought tolerant, the first part of the iris to be sacrificed when water is lacking is the flower. Wait until the top 2 inches of the soil are dry to irrigate, as watering too much can cause root rot.
If a bearded iris is overcrowded, dig up the bulbs and reset them with more space between the plants. Cut back the foliage to about 6 inches before dividing them to make removal easier. Water the plants frequently while they become established.
When planting a bearded iris, the top of the rhizome should just break the surface of the earth. This allows air to circulate around the rhizome and ensures that the plant does not become too moist.
A balance of nutrients is best for the iris. To encourage blooming, apply a 10-55-10 fertilizer in the spring.