If you look hard enough, you can find hardy mums that will come back year after year. Photo: fslandscapesolutions.com
In moderate climates, that is hardiness zones 6 to 9, the most popular fall perennial is the garden chrysanthemum, often called cushion mum, fall mum, or garden mum. In colder climates, though, chrysanthemums haven’t shown themselves to be particularly hardy and many gardeners have learned to treat them as annuals. Fortunately, there are now extra hardy garden mums to try, ones well adapted to climates as cold as zone 3.
How did this change come about? Read on!
Classic Garden Mums
The garden mum does not exist in the wild, but is rather of hybrid origin. It changed botanical names many times over the last three centuries, with the result that there are over 20 synonyms, including two—Chrysanthemum × grandiflorum and Dendranthema × grandiflorum—that are still often used. It took a special ruling of the International Botanical Congress in 1999 to move it back into the genus Chrysanthemum and it is now called Chrysanthemum × morifolium, a name that is unlikely to change. It is believed to have first been hybridized in China over 1500 years ago and there are literally thousands of cultivars.
The main species of chrysanthemum behind the hybrid is the Indian chrysanthemum or golden chrysanthemum (C. indicum), the species used in making chrysanthemum tea, from India and China. It bears yellow, daisy like flowers and indeed, the word chrysanthemum means golden flower.
The Indian chrysanthemums is a not very hardy species (zones 7 to 10). However, many other species have been used in creating today’s chrysanthemum, some of them very hardy (zone 3, 2 and even 1), with the result being that some garden mums are very tender and others very hardy. But until recently, you couldn’t tell which, among the dozens of beautiful specimens sold in the fall in garden centers, were going to act like annuals and die over the winter and which would come back year after year.
That’s changing now, as hybridizers in colder climates, mostly Minnesota and Manitoba, have been working on developing cold-hardy cultivars that will readily overwinter in gardens as cold as zone 3. Here are some examples:
Morden Series (C. × morifolium)
Developed at the Morden Research Station in Manitoba in the 1960s and 70s this series provides compact, densely flowering plants with double flowers, very much the typical cushion mum, only much hardier. They also bloom very early (important in short-season areas), starting in late August, and continue for 8 weeks and more. They’re all about the same size (1-1 ½ ft × 1 ½-2 ft/30–45 cm × 45–60 cm) and are hardy from zones 3 to 9. They’ve been widely used in developing other hardy mums and are the parents of most of the other mums described below. However, they’re becoming very hard to find.
The following varieties are the most popular: ‘Morden Cameo’ (creamy white), ‘Morden Canary’ (yellow), ‘Morden Delight’ (orange-red), ‘Morden Fiesta’ (violet-purple) and ‘Morden Garnet’ (dark red).
Minnesota or Minn Series (C. × morifolium)
Similar to the Morden series, these double-flowered mums were developed at University of Minnesota, a somewhat milder climate than Manitoba. Consider them a bit less hardy (USDA zones 3b to 9, AgCan zones 4b to 9) and somewhat shorter: about 1 foot × 1 foot (30 cm × 30 cm). Among the various cultivars are ‘Minngopher’ (maroon red), ‘Minnqueen’ (bright rose pink), ‘Minnrose’ (deep rose pink), ‘Minnruby’ (ruby red), ‘Minnwhite’ (white) and ‘Minnyellow’ (lemon yellow).
Firecracker Series (C. × morifolium)
This is another series developed in Manitoba, this time by Jeffries Nurseries, by crossing less-hardy hybrid mums with those of the Morden series. They start blooming in early September and continue for 8 weeks or so. They vary in size and form, but all are hardy in zones 3–9.
Dreamweaver® (‘Jefdream’) has semi-double purple flowers with a yellow center. The outermost petals are trumpet-shaped, giving the flower a very original appearance. 2 ft × 2 ft (60 cm × 60 cm).
Firestorm® (‘Jefstorm’) produces semi-double dark red flowers. 1 ft 10 in. × 1 ½-2 ft (55 cm × 45–60 cm).
Power Surge® (‘Jefsurge’) has fully red double flowers. It’s a compact plant forming a wide dome. 1 ½ ft × 3 ft 4 inches (45 cm × 100 cm).
Showbiz® (‘Jefbiz’) produces an abundance of double purplish-pink flowers. 1 ½ ft × 2 ft 6 in (45 cm × 75 cm).
Stardust® (‘Jefdust’) has double to semi-double flowers that are described as “dusty mauve,” but to me open bronze orange melding into deep pink. 20 in × 3 ft (50 cm × 90 cm).
Suncatcher® (‘Jefsun’): bright yellow double flowers. 2 ½ ft × 4 ft (75 cm × 120 cm).
Tigertail® (‘Jeftail’): double orange flowers that become yellow over time. 2 ft 4 in × 3 ft (70 cm × 90 cm).
Developed in Minnesota, these plants result from crosses between C. × morifolium hybrids and the very hardy C. weyrichii. This results in tall, almost shrubby plants with single to semi-double flowers, interesting for the middle or even the back of the flowerbed. Do note though that these plants grow slowly, only gaining their final dimensions of about 4 ft × 5 ft (110 cm × 150 cm) in their third year. This series includes the full range of chrysanthemum colors. Zones 3–9.
The Mammoth™ series was originally launched under the name My Favorite and you may still see some of these plants sold under their former name.
Mammoth™ ‘Red Daisy’ (formerly My Favorite™ ‘Autumn Red’.): Semi-double red with a yellow center.
Mammoth™ ‘Coral Daisy’ (formerly My Favorite ‘Coral’.): Single coral pink.
Mammoth™ ‘White Daisy’ (formerly My Favorite™ ‘White’.): Semi-double white.
Mammoth™ ‘Dark Bronze’ (formerly My Favorite ‘Dark Bronze Daisy’.): Semi-double orange.
Mammoth™ ‘Dark Pink Daisy’ (formerly ‘My Favorite™’ Dark Pink’.): Single deep pink.
Mammoth™ ‘Lavender Daisy’: Semi-double lavender pink.
Mammoth™ ‘Purple’: Single purple.
Mammoth™ ‘Yellow Quill’: Single pale yellow flowers, with the same dimensions as the other Mammoths, but unusual quill-shaped ray flowers.
Despite a name that seems to suggest excellent hardiness, the Igloo series is less hardy than the others mentioned so far, to about USDA zone 5, AgCan zone 6, although they may be worth a try in colder ones with a good mulch. Their double flowers come in the full range of colors and they form the typical dome one expects from a cushion mum. Dimensions: about 2 ft × 2 ft (60 cm × 60 cm).
Other Hardy Garden Mums
The following hardy C. × morifolium cultivars do not belong to any series.
‘Prairie Lavender’ is compact with lavender-pink flowers. The flowers are double, yet you can still see a bit of the yellow center. 2 ft × 2 ft (60 cm × 60 cm). Very hardy (zones 3–9).
‘Matchsticks’ is less hardy than most other “hardy” mums (USDA zones 4b-9, AgCan zones 5b-9), but may be well worth trying because of its very unusual flowers: the rayflowers are yellow-orange and tubular at the base, opening into broader red tips, creating a beautiful contrast. 1 ½-2 ft × 2 ft (45–60 cm × 45–60 cm).
‘Mei-kyo’ is again a less hardy variety (USDA zones 5–9. AgCan zones 6–9). It forms a mounding plant with loose sprays of double pink pompom flowers eventually showing a yellow eye and blooms in mid to late fall. 1 ½-2 ft × 2 ft (45–60 cm × 45–60 cm).
Other Hardy Chrysanthemums
The genus Chrysanthemum was split apart many decades ago into other genera, including Glebionis (annual species), Leucanthemum (typical white daisies), Nipponanthemum (Montauk daisy), Tanacetum (painted daisies) and others. Among the hardier chrysanthemums that remained in genus are the following:
Weyrich Chrysanthemum (C. weyrichii, now more correctly C. zawadskii): this is a dwarf species from the very cold Kamchatka Peninsula and is hardy from zones 3 to 8. It’s a spreading groundcover with low-growing incised leaves that burst into bloom late in the fall, often November. The daisylike flowers can be white (‘White Bomb’ is the usual cultivar) or pink (‘Pink Bomb’), while ‘Apricot’ starts out white, becoming pale pink. The whole plant is rarely more than 6 to 8 in (15–25 cm) high, but can form carpets 2 or 3 feet (60–90 cm) wide or larger and is popular in rock and alpine gardens.
Arctic Chrysanthemum (C. arcticum, syn. Arctanthemum arcticum): This one is much like the previous species. The species has white flowers, but the most commonly grown cultivar, ‘Red Chimo’, a Canadian hybrid, has pink flowers, while ‘Schwefelglanz’ has lemon yellow ones. The arctic mum reaches only 6 to 12 inches (15–30 cm) in height, but forms a compact mat about 12 to 18 in (30–45 cm) diameter. It blooms in early September. It too is popular in rock and alpine gardens. Extremely hardy: zones 1–8.
Rubellum Mum (C. × rubellum, formerly Dendranthema zawadskii latilobum): Also called hardy mum, heritage mum and old-fashioned mum, this has long been the most popular chrysanthemum in cold climates due to its tough-as-nails habit: they don’t call it the hardy mum for nothing! Its background remains mysterious (taxonomists keep changing its botanical name), but that doesn’t stop it from being an easy-to-grow garden mum, well adapted to zones 3 to 8.
It has deeply cut, mid-green leaves, a rather open habit (it is anything but a “cushion mum”) and single daisylike flowers. It’s also a bit of a spreader, thanks to creeping rhizomes, and can be floppy if you grow it in other than full sun. It’s also an early bloomer, at least as fall mums are concerned: usually from late summer into fall. It’s about 2-2 ½ feet (60–75 cm) tall and can spread to well over 3 feet (90 cm) in diameter.
By far the most popular cultivar of this species is ‘Clara Curtis’, with pink flowers, but you will also find ‘Mary Stoker’ (apricot yellow), ‘Princess Margaret’ (bright pink), ‘Duchess of Edinburgh’ (dark pink) and ‘Sheffield’ (pale pink), notably in mail order catalogs.
Growing Hardy Chrysanthemums
Hardy fall mums are perennials and can be grown much like almost any other perennial, although they do have a few particularities worth mentioning.
Planting: Yes, I know: garden centers are full of blooming chrysanthemums in the fall, but ideally, you should purchase and plant garden chrysanthemums in the spring. This will give them to the time to root well before flowering.
If you do buy a plant in the fall in full bloom and plant it as is, it will tend put its energy in producing flowers rather than establishing a strong root system. As a result, even hardy chrysanthemums may fail to survive their first winter. Often, too, you’ll find it lying on its side in early spring, root ball fully exposed, shoved out of the ground by frost heave.
So… if you can’t resist buying a hardy garden mum in full bloom in the fall, you have to be ruthless once you get it home and cut off all its beautiful flowers and buds, but leaving the foliage intact. This will stimulate the plant to produce new roots once you get it into the ground and thus massively increase its chances of survival. Even so, for the first year, you should cover the plant with a really thick mulch of shredded leaves or hay once the ground is frozen.
Exposure: Mums prefer full sun and become a bit thin even in light shade.
Soil: Any garden soil is acceptable, but they prefer a rich, well-drained, slightly acid soil.
Fertilization: Add compost or all-purpose fertilizer regularly: chrysanthemums are rather heavy feeders!
Watering: Chrysanthemums have shallow root systems and won’t tolerate prolonged drought. From spring right until fall freeze-up, water thoroughly whenever the soil is dry to the touch.
Multiplication: Divide in spring or take cuttings in early summer. Their seeds germinate readily, but are not true to type.
Staking: Most hardy garden mums (C. × morifolium) have fairly strong stems and won’t need staking. This is in contrast to the large-flowered exhibition types usually grown in greenhouses where each stem needs to be individually staked. Hardy mums (C. × rubellum) may need staking in partial shade.
Pruning: It used to be said that garden chrysanthemums needed to be cut back by half at the end of June to produce more compact, mounded plants with stronger stems, but most of the varieties recommended here have strong stems and a naturally dense habit, so no summer pruning is required. However, you can prune back dead stems in spring by cutting them at the base. Do not cut back chrysanthemums in the fall! They need their stems to protect them from the cold of winter. People who prune their mums in the fall tend to lose them.
Insects and Diseases: In general, chrysanthemum are not unduly prone to diseases and insects, but you should avoid moistening the foliage when you water to prevent foliar diseases. Chrysanthemum leafminers can trace sinuous trails in the foliage, but are not particularly harmful to the plant’s overall health. If they bother you, simply remove the infested leaves.
Winter Protection: For hardy varieties, leave the stalks still standing all winter so they can catch dead leaves and snow, thus providing their own winter protection. Mums planted in the fall will, however, benefit from a thick protective mulch of chopped leaves for their first winter.
Rejuvenation: Mums are reputedly short-lived plants, requiring frequent rejuvenation by division. While this may be true of some of the older varieties of garden mums (C. × morifolium), it doesn’t seem to apply to many of the hardier types. Certainly, the hardy species (C. weyrichii, C. × rubellum, C. arcticum, etc.) seem to live on and on. And I have clumps of some the Mammoths that are over 15 years old!
If you’re worried about this, though, don’t hesitate to divide them every 2 or 3 years, ideally in the spring.
Where to Find Hardy Mums?
Oddly, local garden centers in cold regions often sell mostly zone 7 or 8 mums in the fall, although you may find some hardy ones tucked away in the perennial section. You’ll probably find a better choice of truly hardy mums (bring up this article on your smartphone) in the spring. Certainly, hardy mums are much easier to find today than 10 years ago.
Many mail-order nurseries also offer a good choice of hardy fall mums.
So, hardy garden mums do exist. It’s up to you now to find and to plant them!
Article updated from one originally published on October 2, 2015.