Mums are most often thought of as seasonal potted plants, something to place on the porch to celebrate fall. But once the ﬂowers fade, the plants wind up in the compost bin. Hardy mums (also known as garden mums) like the Igloo varieties and ‘Sheﬃeld Pink’, however, are tough enough to survive winters as far north as Zone 4 and have a loose, romantic growth habit that looks right at home in a planting bed. Put the plants in the ground now, and with the right care throughout the year, they’ll put on a colorful performance each autumn. Generally, mums bloom from September through November—when the days grow shorter—and stay vibrant for weeks.
Related: What to Plant in the Fall
Plant hardy mums in late summer to early fall—basically, as soon as you see them in garden centers—to give roots a chance to establish before the ground freezes. Loosen the soil around their roots with your ﬁngers, and plant in well-drained soil in a sunny spot. Hardy mums also prefer a soil pH slightly on the alkaline side, so performing a soil test will help you determine where to site your mums. Once planted, water once a week through fall. Let the faded ﬂowers and foliage remain on through winter. (Removing them may stimulate new growth that wouldn’t survive winter.)
Related: Tips for Growing Mums in Containers
As soon as the first hard frost passes, it's time to prepare your mums for winter. Snip stems to 3-4 inches above the ground. Protect plant’s roots from freezing temperatures with a thick layer of straw or shredded hardwood as mulch around the plant base. Doing so will insulate the soil around the plants, ensuring that it will remain a constant temperature instead of freezing and thawing, only to freeze again.
If you get your batch of mums later in the fall season, it might be too late to plant them. That, or winters in your climate may be too cold for mums to keep enjoy (they prefer Hardiness Zone 5 and up). Fear not: You can overwinter your mums indoors. Water the plants well and place in a cool dark area, like a basement or closet. From there, they'll only need to be water about once a week. The mums will eventually "hibernate" and be comfortable in these conditions until spring.
After all chance of frost has passed, prune oﬀ last year’s stems at soil level. Remove mulch around plants and replace with a 10-10-10 fertilizer. While the plants are in limbo before they start blooming again, be sure to keep soil moderately moist and be sure that the bed stays weed-free.
If you had to stow away your mums indoors for the winter, gradually start exposing your plant to light before fully committing it to its place in the ground.
Cut mums back to about half their height—go ahead, use hedge shears—around the Fourth of July to prevent them from getting lanky and ﬂopping over. If you’ve planted one of the Igloo series, wait until after its ﬁrst bloom to trim, then enjoy its second bloom in the fall. Supplement plant with a water-soluble fertilizer to encourage strong branching and bud formation.
Every few years, you'll need to divide your hardy mums to keep them healthy and vigorous. As soon as the last hard frost passes, use a clean spade to dig up your established plant after new growth has emerged. Use the spade to separate all clusters of the plant, separating the vigorous pieces first. Replant your new divisions in a fresh bed.