Hello,

To overwinter iris rhizomes in your basement, Michigan State University Extension (MSU) recommends the following steps:

Dig Up Rhizomes: After the first hard frost, carefully dig up the iris rhizomes.

Trim Leaves: Cut the leaves to about 3-4 inches (7.5-10 cm) above the rhizome.

Dry Them Out: Place the rhizomes in a sunny spot for a day or two until they feel dry to the touch.

Clean Off Dirt: Gently brush off most of the dirt, but avoid washing it completely.

Cure Them: Store the rhizomes in a dark, dry, cool place (around 70°F or 21°C) for one to two weeks to cure.

Apply Anti-Fungal Powder: Dust the rhizomes with powdered sulfur or another anti-fungal powder to prevent rot.

Store Them: Wrap each rhizome in newspaper and place them in a box. Store the box in a cool, dry place in your basement.

Check Periodically: Every few weeks, check on the rhizomes to ensure they are not rotting. Discard any that show signs of rot.

Following these steps, your iris rhizomes should be well-protected and ready to bloom beautifully in the spring!

I hope this helps!