Chrysanthemums, commonly known as mums, are the signature flower of the fall season. If your goal is to plant mums in September so they survive the winter and return next year, the answer is yes, but the timing is tight. Successfully establishing these perennials depends entirely on giving their shallow root systems enough time to anchor themselves before the ground freezes solid. The later in September you plant, the more challenging overwintering becomes.
Why September is the Deadline
The survival of fall-planted chrysanthemums depends on developing a robust root system before hard frost. Mums are shallow-rooted, making them susceptible to frost heave, where freezing and thawing cycles push the plant out of the soil. To counteract this, the plant needs a sufficient period of active growth. Mums require a minimum of four to six weeks of frost-free weather after planting to develop the necessary root mass. Planting in early September allows the plant to focus energy on root growth before shorter daylight hours trigger flowering. Waiting until late September or October significantly reduces the establishment window, lowering the chances the plant will return the following spring.
Choosing Hardy Garden Mums
Selecting the correct type of chrysanthemum is the first step toward successful overwintering. Mums fall into two main categories: florist mums and hardy garden mums. Florist mums, often sold in stores, are bred for showy blooms and are generally treated as annuals with shallow roots ill-equipped for winter. For perennial success, choose a variety labeled as a “hardy mum” or “garden mum,” which are bred to withstand colder temperatures. Look for plants with more green foliage and numerous closed buds rather than those already in full bloom. These hardier varieties, typically suitable for USDA Zones 5 through 9, grow stolons, or underground shoots, which allow them to return year after year.
How to Plant Mums Correctly
Once a hardy variety is selected, planting must be precise to maximize root establishment. If the root ball appears dry, soak it for 30 to 45 minutes. Most nursery mums are root-bound, so gently loosen the compacted roots before planting to encourage them to spread. The planting hole should be dug twice as wide as the root ball but only as deep as the pot. Place the plant so the top of the root ball is level with or slightly higher than the surrounding soil. After backfilling, water the plant immediately and deeply to eliminate air pockets. The new mum should receive about an inch of water per week until the ground freezes.
Preparing Mums for Winter Survival
After the mum is in the ground, winter preparation is crucial. The most important rule for fall-planted mums is to resist cutting back the dead foliage after the first frost. The dried stems and leaves provide a layer of insulation and protection for the plant’s crown throughout the winter months. Heavy mulching is necessary to prevent the cycle of freezing and thawing that can cause root damage. Apply a thick layer of three to four inches of loose material, such as clean straw, shredded bark, or pine needles, over the plant crown. Apply this protective mulch only after the ground has frozen solid, typically in late November or early December, to ensure the plant remains dormant and insulated.