Chrysanthemums, affectionately known as mums, are the defining flower of the autumn landscape, providing a burst of color when most other plants are fading. Achieving a robust and timely fall display requires careful attention during the preceding months of spring and summer. By following specific cultural practices, you can guide your mums to produce a dense canopy of foliage and then trigger a magnificent flush of flowers precisely when the cooler weather arrives.
Maintaining Health During the Summer Months
Establishing a strong, healthy plant foundation in the warmer months is a prerequisite for spectacular fall blooming. Mums thrive in well-draining soil rich in organic matter, as they are prone to root rot if waterlogged. Consistent moisture is important for these shallow-rooted plants, especially during dry periods. Provide about one inch of water per week, soaking the soil deeply at the base of the plant. Avoid wetting the foliage, which can encourage fungal diseases.
Starting in the spring, apply a balanced fertilizer monthly, such as a 10-10-10 formula, to support vigorous vegetative growth. This feeding schedule helps build the strong stems and leaves necessary to support numerous flowers later. Stop all fertilization by mid-summer, typically mid- to late-July or when flower buds first emerge. Continuing to feed the plant with nitrogen past this point encourages foliage growth at the expense of flower buds, leading to a delayed or absent bloom.
The Importance of Pinching and Pruning
Controlling the plant’s shape and bloom time is managed through a pruning technique called “pinching.” This involves removing the soft, terminal growth at the tip of a stem, which breaks the plant’s hormonal dominance. Removing the growing tip forces the plant to produce lateral branches below the cut. This results in a bushier, shorter, and more compact plant that can support more flowers.
To pinch, remove the top one to three inches of the stem, ensuring you leave at least two or three leaves on the remaining shoot. Begin this process in the spring when new shoots are six to ten inches tall and repeat every two to three weeks.
The timing of the final pinch is critical, as it determines when the plant will set its fall buds. The last pinch should occur around the Fourth of July or no later than mid-July. This timing gives the plant sufficient time to recover and prepare for the natural blooming trigger. Pinching later than mid-July risks delaying the bloom or preventing flowering entirely.
How Light Exposure Triggers Blooming
Chrysanthemums are classified as “short-day” plants, meaning their transition to flowering is controlled by the length of the nights. The increase in uninterrupted darkness during late summer and early fall serves as the biological signal for bud formation. The plant needs 10 to 12 hours of continuous darkness each night for six to eight weeks to initiate flower buds successfully.
This requirement for darkness means artificial light sources can easily disrupt the process. Brief interruptions from streetlights or porch lights can trick the mum into perceiving a “long day.” This light pollution prevents the accumulation of hormones that trigger flowering, resulting in delayed or absent blooms. Position plants at least twenty feet away from any nighttime light sources, or use a temporary physical barrier to block the light during late summer.
Troubleshooting and Extending the Flower Display
If your mums fail to bloom on schedule, the most common causes relate to light exposure, pruning, or soil conditions. The plant may not have received the required continuous darkness due to nearby artificial lighting, or the final pinching may have occurred too late in the season, preventing timely bud set. Mums require six to eight hours of direct sunlight each day to produce a dense display of flowers, so insufficient sun exposure will also result in fewer blooms. Overly wet or poorly draining soil can also lead to root rot and stress the plant, inhibiting flower production.
Once the plant is in bloom, maximize the duration of the display by practicing deadheading. This involves removing the faded or spent flower heads, which prevents the plant from putting energy into seed production. Deadheading encourages the plant to divert resources into producing new blooms on its side shoots. Continue to ensure consistent watering, and provide good air circulation to help prevent fungal issues like powdery mildew.