Iris flowers are a beautiful addition to any Minnesota garden. With the right care, these elegant perennials can bring a splash of color to your outdoor space for years to come. To ensure your iris bulbs thrive, it's important to understand the ideal conditions for planting and how often to water them. The best time to plant iris bulbs in Minnesota is when nighttime temperatures range between 40º and 50º.
This gives the bulbs enough time to develop a strong root system before the ground freezes. Place the bulbs in the ground 6 to 8 weeks before this happens. Once established, iris plants generally require an average of 1% moisture per week. During periods of drought (longer than three or four weeks), you'll need to water them deeply every 3 or 4 weeks, depending on the temperature.
In addition to watering, irises should be fertilized in early spring, about 6 to 8 weeks before flowering and again after the flowers have disappeared. This will help ensure they bloom again next year. You can also prevent future problems with iris borers by properly trimming and cleaning your iris plants in the fall. The University of Minnesota Extension provides detailed instructions on how to identify iris borers when inspecting your plants in spring and summer.