September and October are the best months to plant bulbs and rhizomes, including Iris rhizomes. First, select a spot that gets at least 6 hours of sunlight each day. Irises are a full-sun plant, and they will really flourish in a sunny location. Make sure your spot is a well-drained area, because irises need a lot of water but will rot if the area isn’t well-drained. If you don’t have a raised bed, make sure you provide some rows to give the area good drainage. If you’re planting multiple irises, space them about a foot apart. Iris rhizome should be planted with the roots growing downwards and the leaf buds upwards. You should dig your hole about twice the size of your rhizome, and about 3 to 4 inches deep.
Iris bulbs will rot if there are any air pockets or voids in the soil. To get around this, form a mound of soil in the center of your hole. Not much, just a handful or so or soil. Then, place your bulb so that the roots drape down over the mound and the rhizome rests on the top of the mound. Press the rhizome down into the mound, and make sure it makes firm contact with the soil. Now, just fill in the rest of the hole and cover the rhizome with a layer of soil. All you have to do now is water the area thoroughly. This will compress the soil and remove any air pockets.