Chrysanthemums, commonly known as mums, are the quintessential flower of the autumn season, providing a final burst of color as other garden plants fade. These vibrant blooms are valued not only for their rich hues but also for their impressive endurance, often lasting well into the late fall. Maintaining the health of chrysanthemums through the cooling temperatures requires a precise shift in care practices. This guide details the essential daily tasks, post-bloom management, and winter preparations necessary to keep these fall favorites thriving.
Daily Care to Prolong Flowering
A consistent moisture level is one of the most important factors for extending the mum’s fall bloom. Chrysanthemums are thirsty plants, and the soil must be kept evenly moist without becoming waterlogged, which leads to root rot. Potted mums, especially if root-bound, dry out faster than those in the ground, often requiring daily checks to ensure the top inch of soil has not completely dried out. Always direct watering at the base of the plant to keep the dense foliage dry and minimize the risk of fungal diseases like powdery mildew.
Mums are photoperiodic, meaning they initiate blooms in response to the shorter daylight hours of autumn. Despite this, they still require a minimum of six hours of direct sunlight each day during the fall flowering period for optimal growth and bloom quality. Placing them in a location that receives full morning sun is beneficial, as the light helps to quickly dry any dew from the leaves. If sunlight is insufficient, the plant may become leggy and produce fewer, smaller flower heads.
Removing spent or faded flowers, known as deadheading, is a simple yet highly effective way to encourage a longer bloom time. The biological goal of the plant is to produce seeds once flowering is complete, but removing fading blooms interrupts this process. This redirects the plant’s energy toward developing new buds and strengthening its root system. To deadhead properly, snip the faded flower head back to the nearest set of healthy leaves or a developing side bud, which maintains the plant’s tidy, mounded appearance.
Pruning and Nutrient Management
The transition from active growth to dormancy requires a strategic withdrawal of supplemental nutrients. Fertilization must cease entirely by mid-summer, typically no later than July, to prevent the growth of tender, new shoots. Applying fertilizer in the fall encourages soft, late-season growth highly susceptible to damage from the first hard frost. Instead, the plant’s energy should be redirected toward hardening off its existing structure and preparing its root crown for winter survival.
Once the autumn flowering display has finished and the foliage has been killed by a hard frost, a decision must be made regarding post-bloom pruning. One method is to cut the entire plant back immediately to about four to six inches above the ground. This signals the onset of dormancy and helps focus the plant’s remaining resources into the root system. However, this immediate cutback leaves the crown exposed.
Alternatively, many gardeners prefer to leave the dead, brown stalks of the chrysanthemum intact throughout the winter months. This standing debris acts as a natural protective layer, insulating the plant’s crown from harsh weather. For perennial survival, the dead foliage and stems should be removed in early spring, cutting them back to just a few inches above the soil line before new growth emerges. This approach provides the best chance of survival, particularly in colder climates.
Preparing Mums for Winter Survival
Protecting the shallow root system of in-ground mums from the freeze-thaw cycles of winter is the final step in fall maintenance. Once the ground has frozen lightly, applying a thick layer of mulch helps stabilize the soil temperature and prevents the damaging phenomenon of frost heave. Frost heave occurs when repeated freezing and thawing pushes the plant’s root crown out of the soil, exposing it to lethal cold and drying winds.
A layer of loose, airy material, such as straw, pine needles, or shredded leaves, should be placed over the plant’s crown to a depth of three to five inches. This mulch blanket is not meant to keep the plant warm, but rather to keep the soil consistently cold once it has frozen. Avoid using heavy or compacted materials like grass clippings or fine sawdust, as these can hold too much moisture and promote rot around the plant’s crown.
Potted mums require a different strategy since their roots are entirely exposed to the elements. For perennial survival, they should be moved to a cool, dark, and sheltered location, such as an unheated garage, shed, or cold frame. Temperatures should remain consistently above freezing, ideally between 32°F and 50°F. During this dormant phase, water must be drastically reduced, only providing enough to keep the soil barely moist, perhaps once every week or two, to prevent the root ball from completely drying out. If the goal is long-term survival in the garden, any potted mum should be transplanted into the ground at least six weeks before the first anticipated hard freeze for proper root establishment.