Pruning irises every year will help inspire growth for the following year. Proper pruning techniques for irises include: deadheading buds, trimming the stalk, lifting and separating bulb or rhizome clumps and removing any dead sections once the foliage has turned yellow for the season.
Irises store their energy for the next bloom underground in either a bulb or rhizome. Bulbs are spherical in the middle, flatter on the bottom where the roots will grow and have a narrow tip where the stalk emerges. Conversely, rhizomes are elongated and grow sideways.
Once the foliage of the iris has turned yellow for the season, the bulb or rhizome begins gathering energy for its next bloom through the leaves. For this reason, cutting the foliage down to ground level will produce smaller, less-vibrant blooms in the following year.
After three years, you will notice your irises becoming crowded. This signals that it's time to divide the clump of bulbs or rhizomes. To divide: carefully uncover the clump, with a clean garden fork or a sharp knife separate each bulb or rhizome so that it has a healthy bunch of foliage, and replant. Use this time to focus on the soil surrounding your iris plants. Better soil conditions will facilitate better blooms. Irises like well-draining and slightly acidic soil.