Garden mums (Chrysanthemum spp.) are herbaceous perennials in the daisy family and are stalwarts of the flowering autumn garden. When garden centers sell blooming potted mums in the fall, they are usually used as annuals and discarded when the blooms fade. And when gardeners try to transplant these mums into the ground late in the season, chances are they won't make it through winter and become perennial.
However, there are varieties that are truly perennial in most climates when planted in the early spring or in the fall several weeks before the first frost. Their hardiness, plus their ability to be pinched back during the summer so they won't bloom until fall, make these jewel-toned beauties a welcome splash in the garden at a time when most summer flowers have faded. These plants grow fast, and you should have flowers in the first growing season. Bloom times vary with variety and climate from early September through mid-October.
|Botanical Name||Chrysanthemum spp.|
|Common Name||Garden mum, garden chrysanthemum, hardy chrysanthemum, hardy mum, mum|
|Plant Type||Herbaceous perennial|
|Mature Size||4 to 36 inches tall and 12 to 36 inches wide (size varies depending on the variety)|
|Sun Exposure||Full sun|
|Soil Type||Rich, humusy, moist, well-draining|
|Soil pH||6.5 to 6.7|
|Bloom Time||Late summer and fall|
|Flower Color||Gold, white, off-white, yellow, bronze (rust), red, burgundy, pink, lavender, and purple|
|Hardiness Zones||3 to 9|
|Native Area||Asia, Europe|
|Toxicity||Toxic to dogs, cats, horses|
Hardy Chrysanthemum Care
Plant mums as soon as the soil warms in the spring. From late spring to mid-summer, pinch back the tips and flower buds on all shoots to make the plant bushier and prepare it for a dramatic fall show. For optimal blooming, the plants should be fertilized regularly throughout the growing season. After the blooms fade, cut the plants down to about 6 inches, and cover them with straw or another dry mulch to protect the roots over winter. Established plants should be lifted and divided every two to three years.
Mums can make a wonderful impact in containers. But when planted in mixed borders, they will end your garden season with a bang. That's especially true when you pair them with other late-season bloomers, such as sedum, goldenrod, Russian sage, asters, and gaillardia.
Furthermore, because mums flower so late in the season, they are nondescript, though not unattractive, in the garden until blooming time. Thus, they are best planted next to early bloomers. As the spring flowers die back, the mums will fill in and hide their unattractive fading foliage.
Mums thrive in full sun but can handle a bit of shade. Generally, flowering will be most profuse if they are grown in full sun. However, in warm climates, the plants often appreciate some shade during the heat of the afternoon. Mums set buds in response to day length, so avoid confusing them by planting where they might be exposed to bright nighttime light from a patio or window or even a streetlight.
These flowers can handle several soil types, but they do best in rich soil that has sharp drainage. Poor soil drainage will cause the plants to rot. They like a soil pH slightly on the acidic side.
Mums require a lot of water. Give them 1 inch per week during the early growing season, and then increase this to two or three times a week as the flower buds mature and the flowers begin to open.
When growing in a pot, water the soil surface, using a watering can, until moisture begins to drain from the bottom of the pot (make sure the pot has drainage holes). Water should drain freely through the soil and out the bottom of the pot when watering. Soil should remain moist, but not soggy. Soggy soil can cause root rot and other diseases.
Temperature and Humidity
Mums do best in moderate climate conditions. Extreme heat can cause the plants to struggle. And regions with hard winter freezing can see the plants succumb to cold unless they are covered with deep mulch. Mums prefer some humidity, but if the humidity is high, make sure they have good air circulation to prevent rot or disease.
For fall-planted mums to have a better chance of survival in cold areas, you need to give the roots and crown of the plant extra protection. First, leave the foliage on the plants until spring. Do not prune them back after frost has turned them brown. Then, either mulch the plants heavily with at least 4 to 6 inches of mulch or dig up a pot, and move the plants to a more protected spot in the garden for the winter. If you choose to move the plants, do so before the first hard freeze.
In warmer climates, consider heat delay. If you have high temperatures, particularly at nighttime, it can cause the plant to flower later than it usually would. Heat delay can cause irregularly formed flower buds, erratic flowering, deformation of the plant’s crown, and other developmental issues. To bypass this problem in hotter climates, look for cultivars with higher heat tolerance.
It is crucial to provide nitrogen and potassium to chrysanthemums during their vegetative phase. Feed the plants before flower buds form to promote healthy roots, bud development, and a vigorous plant. Start a feeding cycle in March, April, or May, depending upon your zone. You can get a time-released fertilizer (12-6-6), which feeds the plants for about three months. With this fertilizer, you might only need to feed the plants once. The general rule of thumb is to begin after all danger of frost has passed. That way any new growth forced by the nutrients will not be in danger of damage from icy weather. Established plants should not be fed after July, so new growth is not injured by frost.
Varieties of Hardy Chrysanthemums
Many varieties of garden mums have been bred. The original species are often unclear, but horticulturalists generally categorize garden mums by flower shape:
- Anemone: One or more rows of petals with a cushion-like center
- Pompom: Familiar globular shape
- Regular incurve: Petals curve up and in, forming a sphere
- Single or daisy: Looks like its cousin, the daisy
- Spider: Long, curled petals droop down and give a spider-like look
There are also shorter, mounding varieties of mums generally grouped as "cushion" mums.
You will rarely find named mums in garden centers. To obtain the exceptional varieties or exhibition mums, you will need to start from seed or order from a nursery or specialty mail-order company.
- ‘Clara Curtis’ is a long-lasting variety that blooms relatively early in the season with single or semi-double pink flowers.
- ‘Mary Stoker’ is an early season mum with apricot yellow, single-flower heads.
- ‘Apricot Moneymaker’ is a mid-season, anemone-style mum with bronze petals.
- ‘Ruby Mound’ offers an early-season bloom with large, maroon-red flowers
- ‘Patriot’ is a mid- to late-season bloomer with pure white pompom-shape flowers.
- 'Tripoli’ blooms very late in the season and has daisy-like flowers of vibrant pink with yellow centers.
Propagating Hardy Chrysanthemums
You can propagate mums several ways: division, seeds, and cuttings. The most straightforward and fastest method is through division.
- Division: Divide plants that have grown in the garden for at least two years. Younger plants will not have a sufficient root system to survive. By every third spring, divide chrysanthemums to rejuvenate them. Do this in the spring. Pick plants that are at least 6 inches tall. Be careful not to damage the roots. Replant at least 18 inches apart.
- Seeds: Mums can grow from seeds, but it is best if you use purchased seeds. If you attempt to plant seeds from your own plants (most are hybrids), the resulting plant may not be true to the parent. If you are OK with a mystery result, then go for it. Start seed indoors, six to eight weeks before your last frost date, and harden off plants before transplanting outdoors.
- Cuttings: This is an excellent method to get a replica of the plant you have. It does away with the mystery that comes with seeds. Although this method does have extra steps, you have to cut a stem that is at least 4 inches, dip the cut end into a rooting hormone, plant it in a container, wait about four weeks or so for a root to grow and for the plant to grow another 2 inches, then transplant it outside.
Potting and Repotting
Repotting is the single most important thing you can do to increase the longevity of your mums. Most mums are completely root-bound when you get them. The roots have taken up the entire pot, which makes it really hard for the soil to retain any water. To repot, choose a container that is a little bigger than the last container. Fill the bottom of the new pot with good quality potting soil. Break up any roots you can, but do not damage the roots.
When you put the plant in the new pot, the surface of the soil should be an inch below the lip of the new pot. Make sure you have soil, not air surrounding the roots. Tamp down the soil gently. Give the pot a good watering until it flows out of the bottom of the pot.
Growing Hardy Chrysanthemums in Containers
Garden mums are often purchased already flowering in containers. These should be watered daily. Weekly feeding with a diluted water-soluble fertilizer can prolong the blooming.
Unfortunately, the mums for sale in garden centers in the fall have been coddled in nurseries and coaxed to set buds for September blooms. That means they are putting an awful lot of energy into blooming, not growing roots.
Planting these specimens in the garden in late summer or early fall does not guarantee sufficient time for the plants to become established. This is not a problem in warmer climates, where a bit of deadheading will satisfy most mums after bloom, but in areas with sub-zero winters, perennial plants need strong roots to anchor them into the ground. The repeated freezing and thawing of the soil will heave the plant out of the ground and kill the roots.
Common Pests and Diseases
Mums can suffer damage from aphids, thrips, and spider mites. Some signs include leaf and stem damage, webbing on the plants, and visible insects. Common diseases include botrytis, leaf spots, rust, powdery mildew, stem and root rots, verticillium wilt, aster yellows, and viruses. If your plant has visible damage or just seems to be failing to thrive, a disease might be the culprit. Leaf spots and powdery mildew are rarely fatal, but plants with other diseases should be removed and destroyed.