Hardy mums, on the other hand, are highly valued in landscaping because they bloom primarily in the fall, helping you to achieve four-season interest in your landscape. They come in a wide array of colors as well as different flower forms and growth habits. While they are legitimate perennials in moderate climates, hardiness in northern regions is not guaranteed, so hardy mums are often treated as annuals, planted in early fall as potted nursery plants that are already in bloom. Used this way, they provide a pop of color and are then discarded once the cold weather starts to depreciate their foliage and blooms. Hardy mums are fast-growing and will reach their full height within their first year, with the plant filling out a little more each subsequent year. The leaves and flowers of hardy mums are mildly toxic to humans as well as to dogs, cats, and horses. Be sure to plant your mums in a site that’s protected from damaging strong winds. But provide good air circulation around the plants, which can help to reduce the risk of disease, such as fungal infections. For best perennial performance, garden mums require frequent pinching (in the United States pinch plants on or around Memorial Day and Fourth of July), weekly watering, and regular feeding. And in many regions, they will require some special care going into winter. Garden mums become much easier to grow if you treat them as annuals, buying potted plants already in bloom to insert into the fall garden or in containers to replace faded summer flowers. Once they finally fade after a killing frost, you can simply pull the plants from the garden and discard them.

Light

Hardy mums prefer to grow in full sun, meaning at least six to eight hours of direct sunlight daily. However, in the warmer parts of their growing zones, they can benefit from some afternoon shade. The flowers are photoperiodic, meaning they bloom in response to the shorter days and longer nights experienced (in the northern hemisphere) in the late summer and fall. Therefore, don’t plant them near street lights or night lights; artificial lighting can wreak havoc with their flowering cycle.

Soil

These plants grow best in organically rich soil with a slightly acidic to neutral soil pH. Sharp drainage is a must, as soil that remains wet for too long can rot their roots.

Water

Mums like consistent moisture but do not tolerate soggy soil. Water whenever the soil dries out about an inch or two down. In warmer weather and once the plant is large and in bloom, more frequent waterings will likely be necessary. About one inch of water per week is considered a minimum.

Temperature and Humidity

As their common name suggests, hardy mums are hardy to both cold and heat, but the degree of hardiness depends somewhat on the variety you choose, as many have been developed for the conditions of specific regions. Generally speaking, most garden mums can readily handle temperatures up to 100 degrees Fahrenheit, though they’ll need sufficient water and some shade in those conditions. Most hardy mums will continue to bloom as temperatures dip down as low as 20 degrees Fahrenheit; the roots of most varieties can survive winter soil temps down to zero degrees Fahrenheit or even a bit lower. But recent introductions make hardy mums a viable plant even for gardeners in USDA hardiness zone 4, where winter temps can dip down to as low as minus 30 degrees Fahrenheit. Even zone 3 gardeners might be able to grow some varieties successfully. If you live in such a climate, though, it’s important to choose varieties bred for such harsh conditions. Similarly, zone 9 gardeners will want to buy varieties bred for warmer conditions. A moderate humidity level is ideal for these plants. Excessive humidity can encourage fungal disease, such as leaf spots.

Fertilizer

Mums are fairly heavy feeders. You can use a slow-release fertilizer in the spring, following label instructions. Or use a water-soluble fertilizer monthly through July. Any fertilization after July can trigger tender new growth that cold fall temperatures can damage. 

Types of Hardy Mums

Thirteen different classifications of mums are recognized, each with particular characteristics and many named varieties. The most popular categories include:

Anemone: This group features long, flat petals on blooms that reach a maximum size of around 4 inches. Varieties include the light purple ‘Dorothy Mechen’ and ‘Adrienne Mechen’, which have flowers with a pink center that fades to bright white tips. Other varieties include ‘Samba’, with rose-pink flowers; ‘Rhumba’, with coral red flowers; ‘Harmony’, with bright yellow blooms; ‘Overture’, with bright red flowers; and ‘Ruby Mound’ with semi-double bright ruby-red flowers.Pompon: These fluffy mums are also known as button mums. All varieties produce compact blooms in various colors. Some common varieties include ‘Patriot’, ‘Garnet’, ‘Tinkerbell’, and ‘West Point’.Spoon: Named for its spoon-shaped petals, this type of mum grows petite flowers up to 4 inches in diameter. Popular varieties include ‘Kimie’, featuring yellow-gold petals, ‘Matchsticks’, which have yellow centers that end dramatically in bright red “spoons,” and ‘Yellow Quill’.

Historically, garden mums are regarded as hardy only to USDA zone 5, but there are recent introductions by Canadian and University of Minnesota horticulturalists have created many varieties hardy to zone 4, and some even to zone 3. If you live in a northern climate, consider one of these:

My Favorite™ series, developed by the University of Minnesota, is hardy into zone 3b. Plants are up to four feet tall, with coral, pink, or yellow flowers.Morden series, developed in Canada, is said to be reliably hardy into zone 3. Named cultivars include ‘Morden Canary’, ‘Morden Delight’, ‘Morden Fiesta’, and ‘Morden Garnet’.

Other cultivars zone 3 and 4 gardeners can consider include ‘Peach Centerpiece’, ‘Rose Blush’, ‘Sesquicentennial Sun’, and ‘Betty Lou Maximum’, all developed by the University of Minnesota.

Pruning and Pinching

Pinching hardy mums (removing the tips of new growth, thereby stimulating the plants to send out side shoots) requires more maintenance than any other aspect of caring for them. But the effort pays off, because pinching yields compact, bushy plants with profuse blooms. Start pinching in the spring when the new growth has reached roughly six inches long. Every two to three weeks, pinch back half of any new growth when it reaches six inches. Stop pinching chrysanthemums around the beginning of summer, around fourth of July, or else bud formation won’t occur soon enough to ensure flowering for fall. Spent flowers should be deadheaded to prevent the plant from becoming unkempt and to stimulate continued budding.

Propagating Hardy Mums

Hardy mums can be propagated in many ways, but the easiest is by dividing the root clumps in early spring: Mums can also be propagated through stem cuttings:

How to Grow Hardy Mums From Seed

Growing hardy mums from seed is no easy task because the seeds are extremely small and it can take as much as 16 weeks for germinated seeds to develop into mature flowering plants. Furthermore, collecting seeds from existing plants is an unreliable method of propagation, because mums cross-pollinate freely and the plants produced from collected seeds might not be similar to the parent plants. But if you want propagate mums from seed, collect some of the dust-fine seeds from dried heads of spent flowers. A better choice is to buy packaged seeds from a supplier. It’s best to start seeds indoors at least six weeks before the last expected frost date.

Potting and Repotting

Garden mums adapt well to container growing in any well-draining pot filled with ordinary peat-based potting mix. If you live in a climate where garden mums are hardy, you might be able to overwinter the potted plant by moving it to a cold frame or other sheltered location. Otherwise, potted mums can be grown as annuals and discarded at the end of the season. If you are growing potted garden mums as perennials, they will need to be repotted when the plant becomes root-bound, generally every two or three years. Potted mums do not adapt well to being moved indoors to grow as houseplants for the winter. They require some winter chill each year, so it’s best to move your potted mums into a sheltered outdoor location, such as a cold frame or porch, for the coldest winter months.

Overwintering

In warmer climates (USDA hardiness zones 7 to 9), cut the plants back to about six inches after the fall-flowering period has ended. In colder climates (zones 4 to 6), it’s best to leave the top growth in place and also apply a thick layer of dry mulch (straw, evergreen branches) over the plant to protect the crown over winter. In spring, cut off the dead stems to just above ground level. Gardeners in cooler climates sometimes have good results overwintering garden mums by digging up and transplanting them into cold frames for the winter then moving back into their garden locations in the spring. Garden mums are notoriously fickle, so don’t be surprised if your efforts at overwintering are not always successful. Experienced gardeners learn to resign themselves to occasionally losing plants to winter cold.

Common Pests & Plant Diseases

Chrysanthemums have a natural resistance to many insects. In fact, an entire class of natural pesticides incorporates pyrethrin, which is derived from chrysanthemum flowers. But garden mums are still occasionally the target of small insects, such as aphids, thrips, spider mites, and leaf miner. If leaves show deformity, or if you notice fine webbing or trails on leaves, then using an organic pesticide such as neem oil is a good idea. Garden mums can be susceptible to a variety of diseases, including botrytis (a gray mold disease that causes flowers to shrivel), aster yellows (a viral disease that causes yellowing foliage), and several other fungal diseases such as powdery mildew, verticillium wilt, and leaf spots. It can be worthwhile to use a spray fungicide to treat fungal diseases, but often the best approach is to remove affected plant parts—or even entire plants if the disease is widespread. Avoiding overhead watering can help prevent soil-borne diseases from spreading. Fungus only spreads on wet leaves, not dry leaves.

How to Get Hardy Mums to Bloom

Hardy mums will usually provide robust blooms if their basic cultural needs are met: plenty of sun and water, and early pinching back of the stem tips to create bushy rather than leggy plants. Lack of flowering is often traced to deficits in sunlight or water. Unlike many flowering plants that don’t like extra feeding, hardy mums often do respond to extra fertilizer and will produce more and larger flowers.

Common Problems With Hardy Mums

Garden mums are usually easy to grow provided they are given the right conditions, but they are relatively high-maintenance, so don’t be surprised if some problems do arise. This is not a plant-it-and-leave-it specimen.

Yellow Leaves

Yellowing leaves on garden mums is very often a sign of a viral or serious fungal disease. The best solution is to cut away all affected plant parts—or even remove and destroy the entire plant before the problem can spread.

Leggy, Droopy Plants

If mums are not severely pinched back as they first begin to grow in the spring, the plants can easily develop long, leggy stems that collapse under their own weight. For best results, hardy mums should be pruned or pinched back severely at least twice in spring and early-summer before the late summer and fall blooming season gets underway. Pinching back the plants will keep the plants from getting too tall and leggy. Remember, too, that garden mums need a lot of sun, and if they are planted in shady conditions, the natural tendency will be for the stems to stretch in an effort to reach for more sunlight.

Plants Break Off at the Soil Line

It can be tricky to get the watering routine right with these plants. They need regular, reliable watering, but too much water, especially in soil that is too dense or has too much clay, can cause root rot that will soften the stems and cause the plants to break off. Make sure to adjust your watering routine based on how much natural rainfall is occurring. More than one inch per week might put your plants at risk of root rot.