How to Grow Garden Mums

Buy garden mums, and plant them in spring

The potted mums sold by the thousands in September are usually treated as fall annuals. That works for a season of porch color, but if you want mums that return, two choices matter.

Pick garden (hardy) mums, not florist mums. Florist mums need long uninterrupted nights to flower, so outdoors they bloom so late that freezes often destroy the buds. Iowa State notes that most do not survive winter, and the few that do rarely bloom. Garden mums are hardier and bloom by early fall. In Wisconsin, Extension recommends early varieties that bloom in August or September; later October bloomers work only in the southern part of the state.

Plant in spring. Iowa State calls spring the best time, because mums planted in late summer or fall often lack time to root before winter. Purdue’s target in Indiana is mid-May, when peonies and iris bloom, and notes that fall planting has not proven satisfactory in most of the state. In the South the rule relaxes. Clemson lists both fall and early spring for South Carolina, where mums are hardy, but still finds spring plants fuller. The dates for your zone above show when frost danger ends where you live.

If you do plant a fall mum, water it regularly for the next 2 to 3 months, as Iowa State advises for any new planting, and give it the winter protection described below.

Site, soil and spacing

Mums need full sun, at least 6 hours a day. NC State suggests some protection from afternoon sun in hot climates. In shade the stems sprawl and the flowers are fewer and smaller. Keep mums away from outdoor lights, which can stop flowering.

Drainage is critical, especially for winter survival. Wisconsin Extension says mums that sit in wet soil are likely to winterkill. Work 2 to 4 inches of compost or other organic matter into the bed, and aim for slightly acid soil around pH 6.5, as Purdue suggests.

Set plants at the same depth they grew in the pot. Space tall, spreading types 18 to 24 inches apart and compact cushion types about 12 inches apart.

Pinching: the key to bushy mums

Unpinched mums grow tall, flop open and flower only at the stem tips. Pinching removes the growing tip and makes the stems branch, which gives a compact mound covered in buds.

Iowa State’s method is to pinch out the tips when new shoots reach about 6 inches, then pinch each new side shoot when it reaches 6 inches. Illinois Extension starts two weeks after spring planting.

The last pinch date depends on where you garden, because mums need several weeks after the final pinch to set buds:

• Upper Midwest and North: stop by about July 4 (Iowa State). Wisconsin stops by mid-June for early varieties, late June for late-September bloomers and early July for early-October bloomers.
• South Carolina: pinch about every four weeks until early July in the upper Piedmont and mountains, or until early August on the coast (Clemson).
• North Carolina and Florida: NC State makes the last cut around mid-August. UF/IFAS prunes from late spring through mid-August.
• South Texas: pinch monthly from May through July, with the last pinch no later than August 15 (Texas A&M).

Pinching late delays bloom and can prevent it entirely if frost comes first.

Watering and feeding

Water deeply during dry spells, soaking the soil to 5 or 6 inches. Purdue warns that frequent light watering keeps roots shallow and encourages mildew, Septoria leaf spot and Verticillium wilt. Water at the soil and keep the foliage dry.

Mums are heavy feeders. Purdue works a complete fertilizer such as 10-10-10 into the bed before planting and adds a second light application in midsummer. Clemson recommends a weekly soluble fertilizer for South Carolina plantings. Wisconsin feeds every 7 to 10 days until early August. Stop once buds form, around late July or early August.

How mums decide when to bloom

Mums are short-day plants. Purdue explains that most cultivars begin forming flower buds once days drop below about 12 hours, then open 6 to 8 weeks later. Catalogs sort them into early (August-September), mid-season and late (October) types.

Florida gardeners see a different pattern. UF/IFAS notes that mums there bloom whenever days are short, from fall through spring.

Helping mums survive winter

Mums have shallow, fibrous roots, and repeated freezing and thawing heaves them out of the ground. To improve survival in cold regions:

1. Choose early-blooming, proven hardy cultivars. Iowa State notes that many University of Minnesota introductions do well there.
2. Stop fertilizing in summer.
3. Leave the old stems standing through winter. Iowa State reports better survival than when plants are cut down.
4. After the soil freezes, usually in late November or early December, cover plants with several inches of straw or pine needles. Purdue waits until after 2 or 3 nights below 20°F. Avoid tree leaves, which mat down.
5. Remove the mulch in early spring, typically late March or early April in Iowa.

In San Antonio, Texas A&M suggests treating garden mums mainly as annuals. If you want to keep them, cut off the frost-killed tops and mulch 3 to 4 inches deep.

Dividing and propagating

Mums spread quickly and decline when crowded. Divide clumps every 2 to 3 years, or every year or two in South Carolina, in early spring as new growth appears. Purdue suggests doing it 3 to 4 weeks after the last killing frost. Discard the woody center and replant outer sections that each have several shoots and good roots.

Cuttings are easy too. Take the top 3 to 4 inches of non-blooming shoots in spring or early summer, dip them in rooting hormone and stick them in sand or perlite. They root in 4 to 5 weeks. Seed is used only for breeding, because seedlings do not come true.

Varieties for the South

For South Carolina, Clemson recommends dozens of cultivars, including the early white ‘Chablis’, the heat-tolerant yellow daisy ‘Allure’, the long-lasting yellow ‘Jessica’, the early maroon ‘Ruby Mound’ and the Belgian Mum series. For fall-garden companions, Illinois Extension suggests Miscanthus grasses, fall asters such as ‘Purple Dome’ and the goldenrod ‘Fireworks’, as a design pairing rather than a pest benefit.

Common problems

• Tall, floppy plants: caused by no pinching or too much fertilizer. Pinch in spring and early summer.
• Winter kill or heaving: caused by poor drainage, late planting or freeze-thaw cycles. Plant in spring in well-drained soil and mulch after the ground freezes.
• Aphids and spider mites: worst in hot, dry weather. Spray insecticidal soap with thorough coverage and repeat as needed.
• Leaf spot and powdery mildew: remove infected debris, space plants for air flow and water at the soil.
• Verticillium wilt: leaves pale, brown and hang on the stem. Do not take cuttings from infected plants or replant mums in the same spot.