Feed with a low nitrogen fertilizer ie. bulb food.
Allow the soil to dry out between waterings.

When I re-dig a bed I add bonemeal or superphosphate.
Bonemeal takes longer to become available to roots.
Superphosphate is available immediately so there should be neutral (?) soil between it and newly planted iris. It can burn new roots.

Altho most beardeds have strong stems, not all. And Mother Nature does send rain at inopportune times. Good drainage is very important.