Perennial Mums: How to Overwinter Mums

The Best Time to Plant Mums

In October, chrysanthemums and asters are everywhere, from six-inch pots to bushel baskets of orange, yellow, pink, and copper mounded behemoths. I just want to buy everything and plant!

Then I slap myself on the forehead, take a deep breath and cry “You really should have planted these in May!” People start pointing at me and make avoid-the-crazy-woman sounds to their children and spouses. I slink off to the refuge of my car or the plumbing department to avoid further embarrassment.

It’s true: the best time to plant mums is in the spring. It gives them plenty of time to put down roots, gather sunlight in the summer, bloom profusely in autumn, and get ready for the cold season ahead. But that doesn’t mean it’s impossible to plant them in autumn and have them return next year, too. It just takes a little extra work!

Why Mums Don’t Often Last Through Winter

Chrysanthemums are a hardy perennial plant, but those that are sold in garden centers in the autumn are most often treated as annuals. They are already in full bloom with beautiful autumn jewel-hued colors to decorate your house, along with autumn wreaths and gourds. Once a flower is in full bloom, it’s actually past its peak and already declining. (Be sure to buy mums with lots of unopened buds so that they last longer into the fall season.)

If these plants are put in the ground past mid-October, many won’t make it through the winter in areas where temperatures dip into the single digits during the winter months. This is because mums that are planted late in the growing season are near or at the flowering stage, and they won’t put energy into growing roots to sustain themselves through the winter. All the energy is put into blooming.

That’s why mums are best planted in spring or earlier in the fall, as they’ll have more time to get their roots in the ground before winter’s chill comes along. 

Gardeners in areas where temperatures often dip below zero (Zones 4 and colder) can lose even spring-planted hardy mums to winter, however. You can changes the odds in your favor by leaving the dead foliage on mums and asters instead of shearing them down for neatness. An Iowa State University study found that unpruned plants survive at much lower temperatures than those that were pruned; the foliage acted as extra insulation. Be sure to add 4 to 6 inches of mulch after the ground has frozen for even more protection.

Potted mums from the florist or grocery store, as well as exotic or annual types (like huge Football chrysanthemums, delicate Spiders, and Spoons), are not as well suited to survive cold winters either and are generally not good choices for landscapes. They are not bred to be hardy; it’s their form, color, and size that are prized. Think of them as disposable holiday decor, along with the pumpkins you buy for Halloween or otherwise.

How to Overwinter a Mum

If you live in Zones 5 to 9, where the mum is naturally hardy, the best way to overwinter your mums is by planting them in the ground by late September. In most areas they won’t need any extra winter protection, but in Zone 5 it’s a good idea to put down a 2-4 inch layer of mulch around the plants.

If you live in a colder region (Zones 4 and colder) or it’s already October, your best bet is to overwinter your potted mums indoors in a cold, dark place. Here’s how:

1. If the plants are in the ground, pot them up after the first fall frost; include as much root system as possible. Leave the foliage on the plants.
2. Water well and place in a protected area where it is totally dark and 32º to 50ºF. An unheated basement or a dark, cold closet work well.
3. The plants will hibernate for the winter as long as you keep their roots from drying out. Check pots weekly and water enough to keep soil lightly moist; remember that they won’t be using much water while hibernating, so be careful not to overdo it!
4. In the spring, acclimate plants to light gradually and set them out in the garden after the last killing frost. Cut down the old leaves and stems once you see new foliage emerge.

With a bit of forethought and care, you can keep your mums blooming year after year!

Want to read more about mums? Check out our Growing Guide for Chrysanthemums for growing and care tips.

All About Fall

Want more autumn? See our Autumnal Equinox page for fall-themed advice, folklore, and fun, and read our Fall Weather Forecast to see what sort of weather to expect this autumn!