Irises are easy-to-grow perennials, making them a favorite of home gardeners. The bearded iris, with its furry stripe, is the most common type. Beardless irises include the large-flowered Japanese iris and the Siberian iris with narrow blooms. You can grow irises from seeds or, more easily, from the tuberous roots called rhizomes. Follow these steps to grow irises from rhizomes.
Choose a location in the full sun or partial shade. Most irises like full sun. Plant them in partial shade only in a warm climate.
Prepare the soil. Irises require good drainage. Till down 12 to 18 inches and mix in compost, peat or sand to avoid root rot. In clay soils, consider raised beds.
Divide the long rhizomes into sections, each with one or two leaves growing up and several roots growing down. Dig shallow holes about 18 inches apart, and mound soil in the center of each hole. Place each rhizome section on the mound and arrange the roots so they hang down. Fill the holes so the roots are fully covered and the rhizome rests no more than 2 inches below the surface of the soil. Firmly press down the soil.
Cut off old stalks at ground level after flowering. Leave the green foliage intact. Remove the dead leaves from the base of the plant.
Divide your irises and replant every three years. This prevents overcrowding and root rot. The best time to dig and separate is usually in late summer after the iris has finished blooming.
Dig up the rhizome and wash off the soil. Divide and discard the old or soft sections. Let dry for a day and replant. Amend the soil with compost before planting.
Tips & Warnings
- Different species of iris have different care requirements. Consider the species before planting.
- Once irises have been in the ground for a year, fertilize occasionally with a good garden fertilizer low in nitrogen. Bone meal is also good for irises.
- Mulching helps with weed control. In colder climates, mulching in winter helps protect the plant.
- Water thoroughly. Once established, bearded irises need water only occasionally. Japanese and Louisiana irises require moist conditions in summer.
- Irises are susceptible to iris borers. These tiny caterpillars become moths in the fall. Check in the rhizomes for holes that will cause the iris to rot. Sawdust piles around the plant base are a sign. Treat with insecticide. To prevent, clean up debris before winter.
- Irises are very susceptible to root rot. This is why a well-drained soil is so important.
- Don't mulch during the growing season. This will contribute to root rot.
- Don't plant too deeply. You want the irises to come up in the spring.
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