In Minnesota, the ideal planting season for iris bulbs is from mid-September to mid-October. This allows the bulb to take root and ensures that the irises will bloom best in full sun, which means at least 6 to 8 hours of sunlight a day. Although they can tolerate as little as half a day of sun, it's not ideal. Other plants should not shade bearded lilies; they do better in a special bed on their own.
When it comes to planting, the best time is from late summer to early fall. Depending on your location, we recommend planting from mid-July to mid-October. Those who live in southern climates tend to delay deadlines and plant until November. Spring planting can be done under abnormal circumstances, but it often results in a lack of flowering for a season or two and slow establishment.
Once the iris begins to diminish its flowers, it's time to start digging them up and leave more room for the plants to grow underground. An ascending rhizome looks like a tangle of snakes at the base of the plant. Summer has reached its peak and the iris is fading; this is when plants know it's time to get up and move and will begin to show signs of distress in late summer if they need to be dug up and divided before the first frost destroys them. The Siberian iris is still one of the easiest iris plants to grow; some flowerbeds continue to bloom for decades without any division or insecticide, forming a large stripe of blue, lavender, white or one of the new multicolored colors.
Resistant bulbs or bulbs that bloom in spring require a cold period to break their dormancy and begin the development of spring flowers. BlomsBulbs sells a mix of what they call English iris bulbs (iris latifolia) that includes purple, white, blue and mottled irises. The large bearded iris (from a rhizome, often called German iris), the bulbous iris (correctly, the Spanish or Dutch iris), the English iris found in the Pyrenees; the beautiful and thin Siberian iris; and the Japanese iris, which looks similar to the Siberian iris but has different requirements. An advantage over the bearded iris, the English iris blooms later in the year and blooms in June and July.
Schreiner's, one of the largest producers of irises in the world, warns that irises should not receive too much water because it causes rot. Unlike other types of irises that grow from thickened roots called rhizomes, Dutch irises grow from teardrop shaped bulbs that are planted in the fall.The Dutch iris (Iris Hollandica) has orchid-like flowers with silky petals and blooms later than the bearded iris. It is grown from a rhizome and is a mostly carefree garden staple, except for the dreaded irise-borer caterpillar.The best time to dig up iris bulbs or rhizomes in Minnesota is between late summer and early fall. This will ensure that your plants have enough time to take root before winter sets in.