The Magic Valley Iris Society (MVIS) is a Non-Profit organization that was first formed in 1956. Our ongoing goal is to educate the public to the iris culture and to share the joy and beauty of growing irises. Read the MVIS Brochure (here).
Planting and Growing Irises:
Irises are among the easiest of perennials to grow, and they give an abundance of beauty with minimum care. The iris has a thick fleshy root called a “rhizome” (pronounced rye-zome) about like a tough potato in texture. When you buy a new iris, you will probably receive a rhizome with clipped roots and leaves. It can remain out of the ground for a week or two without serious harm, but the sooner it is planted, the better. It helps if you soak the rhizome overnight in water just before you plant.
To plant your irises, choose a sunny spot in well drained soil. Prepare soil well by spading or turning over the soil with a garden fork to a depth of at least 10 inches. Spread fertilizer and work it into the top of the soil. A well prepared bed will result in better growth and more bloom. The soil should be light. If it is clay soil, add very coarse sand and humus. Bone meal and a good garden fertilizer, low in nitrogen, are good for irises, but manure should be used only after it has aged for about a year. Otherwise, it may cause rot. The roots must be buried firmly to hold the plant in place, but the rhizome should be near the surface.
If you have several plants, plant them at least a foot and a half apart, “facing” the same way. The rhizomes will then increase in the same direction, without crowding each other too soon. In about 2 or 3 years, the new rhizomes will begin to crowd each other and you will want to divide the plants.
You will have so many new rhizomes that you can share them with your friends and neighbors. Perhaps you received your first rhizomes from a friend. When digging, keep all plants carefully labeled with their names, for sure identification. It is wise to keep diagrams of your planting area to double check individual labels on the plants.
The digging and separating is best done between one and two months after bloom season, usually in July or August for this Idaho area. Soon after this the irises grow roots which help to hold the plant firmly during the winter in areas where freezing and thawing can result in heaving the rhizome out of the ground. Some member’s mulch in the winter but you will want to remove the mulch early in the spring to prevent rotting of the rhizomes.