Just when summer-blooming plants fizzle, these chrysanthemums will produce a profusion of flowers as the days grow shorter. And unlike the potted or florist mums used for fall decorating, they will return after the winter to add late-season color in your garden beds again and again.
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. With the right care throughout the year, they’ll put on a colorful show each autumn. Generally, mums bloom from September through November—when the days grow shorter and weather cools off—and stay vibrant for weeks. Here are five tips for how to grow hardy mums so you can enjoy their beautiful fall flowers for years to come.
1. Plant Hardy Mums in Spring
Even though you'll start seeing mums in garden centers in late summer, if you plant them at that time of year or later, it's unlikely they would survive the winter. You'll have more success when you plant hardy mums in spring after the last frost to give roots a chance to establish before the colder months. Place them in well-drained soil in a sunny spot. They prefer a soil pH slightly on the acidic side, so performing a soil test will help you determine if you need to add an amendment to your soil to adjust the pH. Once planted, water once a week through fall.
Editor's Tip: Local chapters of the National Chrysanthemum Society often hold spring sales where you can find interesting varieties at the best time to plant them.
2. Prepare Your Mums for Winter
As soon as the first hard frost occurs in your garden in fall, it's time to get your mums ready for winter. Don't cut away the faded ﬂowers and foliage—removing them may stimulate new growth that wouldn’t survive a freeze. Protect their shallow roots with at least a 3-inch-thick layer of shredded leaves or hardwood mulch around the plant's base. This will help insulate the soil, ensuring that it will remain a constant temperature instead of freezing and thawing, only to freeze again. All those temperature swings can stress the plants, and even heave them right out of the ground, so the more you can protect them from this, the better.
What about the potted mums you can buy already blooming in autumn? Try overwintering them indoors. First, cut off the stems at pot level, then place the pots in a cool dark area, like a basement or closet. Water about once a week, just to keep the roots from completely drying out. The plants will go dormant until spring, when you can set them outside again once temperatures stay above freezing.
3. Prune Last Year's Stems in Spring
After temperatures remain above freezing, use sharp pruners to cut off last year’s stems at soil level. Remove mulch around plants and add a little 10-10-10 fertilizer or a big helping of compost to fuel new growth. While the plants start growing, be sure to keep soil moderately moist and be sure that the bed stays weed-free.
If you stowed away your potted mums indoors for the winter, gradually start exposing your plants to light before planting them outdoors. Once planted, water and feed as you would other mums in your garden.
4. Trim Back Mum Foliage and Fertilize in Summer
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 with a water-soluble fertilizer to encourage strong branching and bud formation.
5. Divide Plants for Healthy Longevity
Every few years, you'll need to divide your hardy mums to keep them healthy and vigorous. In spring, dig up your established plant after new growth has emerged. Use the side of a spade to separate the plant's root ball into several pieces. Replant your new divisions and water them in well.