The purchase of a chrysanthemum, or “mum,” often signals the start of the autumn season, bringing vibrant color to porches and patios. For the plant’s long-term health, repotting or planting out is generally necessary immediately after purchase, especially for those acquired from big-box stores or supermarkets. While some mums are seasonal annuals meant only for temporary display, the perennial garden varieties benefit significantly from being moved to a larger container or the ground. This simple act is often the deciding factor in whether the plant thrives for a season or returns for many years.
Why Store-Bought Mums Need Immediate Attention
Mums sold in garden centers and grocery stores are often severely root-bound, meaning the roots have completely filled the container and are growing in tight, circling patterns. This condition prevents the plant from absorbing sufficient water and nutrients because the dense root ball acts like a sponge that dries out quickly and is difficult to rehydrate. Ignoring this root confinement leads to stunted growth, rapid wilting, and a significantly shortened lifespan once the plant is brought home.
It is important to distinguish between the two main types of mums available: “florist mums” and “garden mums”. Florist mums are specifically bred for dense, abundant flowers and are typically treated as annuals, often having very shallow root systems that are not cold-hardy. Garden or hardy mums, however, are perennial varieties intended to survive the winter and return each spring, making them the only type that benefits from being planted into the garden. Garden mums need the space and time to establish a robust root system, which an immediate repotting allows them to do.
Choosing the Right Time and Location
The most favorable time to plant perennial garden mums is in the spring after the last frost, giving the plant an entire growing season to establish its root structure. If planting in the fall, which is when most mums are purchased, it is best to do so at least six weeks before the first hard frost. This period is necessary for the roots to anchor themselves and prepare for winter dormancy, increasing the plant’s chances of survival.
Mums require a location that provides full sun, meaning they should receive a minimum of six hours of direct sunlight each day for optimal blooming and health. The soil must be fertile and, most importantly, very well-drained, as chrysanthemums are highly susceptible to root rot in soggy conditions. If planting in the garden, amending dense or clay-like soil with organic matter, such as compost, will significantly improve drainage.
The Step-by-Step Repotting Process
The first step is to choose a new container that is about two inches larger in diameter than the original nursery pot, or prepare a planting hole for ground placement. Gently remove the mum from its container, which will likely reveal a solid, tangled mass of roots that has taken the shape of the pot. These roots must be loosened, a process known as “teasing” or “scoring,” to encourage them to grow outward into the new soil rather than continuing to circle.
Use your fingers to gently pull apart the bottom and sides of the root ball, or use a sharp knife to make shallow, vertical cuts in three or four places around the outside of the root mass. This intentional damage signals the plant to produce new, outward-growing roots. Plant the mum at the same depth it was in the nursery pot, ensuring the crown is level with the surrounding soil. After planting, water the area thoroughly until water runs out of the drainage holes or the ground is saturated, which helps the soil settle around the newly teased roots.
Long-Term Care for Established Mums
Once established in their new home, perennial garden mums benefit from a practice called “pinching” during the spring and early summer growing season. Pinching involves removing the top half-inch to inch of new growth from each stem, which encourages the plant to branch out and develop a bushier, more compact shape. This practice should generally cease around early to mid-July to allow flower buds to form for the autumn bloom.
Consistent watering is necessary throughout the summer, ensuring the soil remains evenly moist but never waterlogged. Once the plant has finished blooming and the foliage has been killed by a hard frost, cut the stems back to about four to six inches above the ground. For perennial varieties, applying a layer of light, airy mulch, such as straw or evergreen boughs, after the ground freezes can help insulate the roots and protect them from the stress of freeze-thaw cycles over the winter.