No, you do not need to soak iris bulbs before planting. If they already have rhizomes, however, soaking can help loosen them up, making them easier to work with and easier to plant into the ground.

Bearded irises (Iris germanica ... inches and do not compost but trash. Remove any dead or diseased foliage, spent flowers, weeds, and any fallen leaves. Bearded irises grow from rhizomes.

“Passalong plants” — a term with its own roots in many an old family garden.