08/12/2026
Per usual, great information from our friends at Iowa State Extension Yard and Garden !
While most perennials are best divided in early spring, late summer/early fall (September in Iowa) is a good time to dig and divide peony, daylily, garden phlox, hosta, lungwort, ornamental onion, and hardy geranium.
Late summer/early fall division gives the plants several weeks to get re-established in the landscape before winter. Perennials divided at this time should be mulched with several inches of straw or pine needles in mid to late November. Mulching helps prevent repeated freezing and thawing of the soil (during the winter months) that can heave plants out of the soil.
See this extensive list for the best times to divide other perennials: https://yardandgarden.extension.iastate.edu/how-to/how-divide-and-transplant-perennials
Iowa State University Extension and Outreach ISU Extension and Outreach - Agriculture and Natural Resources