Hardy Mum Plant Profile

Yellow mums as a backdrop to ornamental kale
David Beaulieu

Hardy mums not only come in many different colors, but they also have different flower forms and growth habits. For instance, the popular "cushion" type has a compact growth habit. The shape and arrangement of the petals of a mum's blooms can also vary from group to group. The most popular flower form is the "decorative," which is so packed with long, broad petals that you can hardly see the center. Along with such diversity, the plants' late blooming period makes them a must-have in the Northerner's fall garden.

  • Botanical Name: Chrysanthemum morifolium (Chrysanthemum coming from the Greek, chrysos, meaning "gold," plus anthos, meaning "flower")
  • Common Name: Hardy mums, garden mums
  • Plant TypeHerbaceous plant with a perennial life cycle
  • Mature Size: About 2 feet high (but varies by cultivar)
  • Sun Exposure: Full sun
  • Soil Type: Well-drained, evenly moist, and rich
  • Soil pH: Slightly acidic to neutral
  • Bloom Time: Usually geared for a late-summer or fall bloom time through pinching
  • Flower Color: Gold, yellow, bronze (rust), red, burgundy, pink, lavender, purple, off-white, and white
  • Hardiness Zones: 3 to 9
  • Native Area: Asia and northeastern Europe

How to Grow Hardy Mums

Growing these plants for optimal display value requires getting a few things right. They are fussier to grow than many other plants. It all begins with realizing that there are cultivars considered "hardy mums" and cultivars considered "florist mums." Hardy mums put out stolons. Florist mums put out few or no stolons and are less likely to over-winter in cold regions.

If you garden in the North, buy cultivars that are hardy mums in your area unless you don't mind treating them as annuals. For you, "hardy mums" has to be more than a nickname: It is what you truly need. The hardiness of Chrysanthemum morifolium varies greatly, depending on the cultivar or the nursery series.

Since it is so important to know what cultivar you will be working with, it is wiser to buy mail-order hardy mums (single-stemmed rooted cuttings) from a catalog in spring rather than buying potted mums from a farm stand in fall that are already blooming. In a good catalog, you have all of the relevant information in front of you, including which types are the hardiest. An example of a nursery series that is hardy is Mammoth.

Another benefit of buying from a catalog is that you can plant your mums in spring. Spring planting gives the plants longer to become established, thereby improving their chances of surviving the winter. Choose a location where they will be sheltered from winter winds.

Once you have selected chrysanthemum flowers suitable for your area and planted them, you have to care for them properly. Do not overcrowd chrysanthemums: Good air circulation reduces the chance of disease. By every third spring, divide chrysanthemums to rejuvenate them. Hardy mums will be even hardier with winter protection. Mulch them for winter. If you can't locate them where they will be sheltered from winter winds, then you should build a modified version of the shrub shelters used for winter protection for shrubs. Do not prune the plants in fall: Existing branches offer the roots protection.

Pinching hardy mums requires more maintenance than any other aspect of caring for them. Pinching yields compact, bushy plants with more blooms. "Pinching" means removing the tips of new growth, thereby stimulating the plants to send out side-shoots. It is called this because, on non-woody plants, you can generally accomplish the task simply by grasping the stem (at the targeted spot) between thumb and forefinger and severing it with a pinching action.

Start pinching in the spring when the new growth has reached 4 to 6 inches in length. After that, every 2 to 3 weeks, pinch the center out of any more growth when it reaches 6 inches. But stop pinching chrysanthemums around the beginning of summer, or else bud formation will not occur soon enough to ensure flowering for fall.

You also have to be ever-mindful that, while chrysanthemum flowers hold up against light frosts, hard frosts will damage the blooms that you have worked so hard to produce. Your pinching activities, then, must be balanced with the fact that you are in a race against time to get blooms before fall's first hard frost: That is why it is so important to stop pinching at the right time, based on the cultivar you have. Stop pinching:

  • Early-blooming cultivars by mid-June
  • Cultivars that bloom in September by late June
  • Cultivars that bloom in October by July 4

Light

Grow hardy mums in full sun in the North. In the South, however, they can profit from being grown in light shade. Chrysanthemum flowers are "photoperiodic": They bloom in response to the shorter days and longer nights experienced (in the Northern Hemisphere) in fall. Therefore, do not plant chrysanthemum flowers near street lights or night lights: The artificial lighting may wreak havoc with their cycle.

Soil

In the North, it is critical to provide mums that you wish to grow as perennials in a well-drained soil. This is because it is not just cold temperatures that can kill mums in winter but also poor drainage.

Water

During the growing season, check to ensure that the soil throughout the root zone is evenly moist.

Fertilizer

Fertilize in spring with a slow-release fertilizer. The NPK value of the fertilizer should be 12-6-6. The benefit of using a slow-release fertilizer is that you only have to fertilize once per year.

If you use a fertilizer that is not slow-release, you will have to fertilize multiple times each year, as follows:

  • Fertilize your hardy mums once each month in spring from the time that they first come up.
  • In summer, fertilize once in July.
  • Do not fertilize after July. Any new growth put on after July would be too late to harden off for winter.

Uses for Mums

Chrysanthemum flowers have traditionally been boiled in China to make a tea, used in folk medicine for influenza patients. In landscaping, chrysanthemums are valued for the fact that they bloom in fall, helping you to achieve four-season interest in your yard. They look best planted in a mass (but for plant health, do not overcrowd). Chrysanthemum flowers are also a favorite of florists for arrangements, due to the longevity of their blooms.

Buying Potted Mums in Fall

Despite the benefits of buying mums from a catalog and planting them in spring, potted mums are sold by the millions at nurseries in fall. Their allure is understandable: Consumers eager for fall decorating see them in bloom at the nursery and think "instant display."

But, first of all, what you are buying, in this case, are not necessarily cultivars meant to grow locally as hardy mums: They may only be meant to be displayed for a short period. Secondly, because these chrysanthemum flowers are bought specifically for fall flower displays, even folks living in zones warm enough for them to be perennials often fail to plant them early enough to allow them to become established. They should be planted at least 6 weeks before a killing frost, and even that may not be soon enough.