Chrysanthemums (mums) are a favorite perennial that brings vibrant color to gardens, particularly in the fall. While these plants are generally robust, they tend to become woody, leggy, and less productive after a few years. Propagation is the most reliable way to refresh older plants and ensure the exact characteristics of a specific cultivar, as plants grown from seed often do not resemble the parent. By learning to create new plants from existing stock, gardeners can easily and inexpensively expand their collection of these classic flowers.
Propagation by Stem Cuttings
Propagating chrysanthemums from stem cuttings is the preferred method for generating new plants that are genetically identical to the parent. The most successful time to take these cuttings is from late spring through early summer, ideally before any flower buds have begun to form. Select healthy, non-flowering shoots that are in the softwood or semi-hardwood stage of growth, as this material has the highest regenerative capacity.
Using a sharp, sterilized blade, take cuttings that are approximately two to four inches long, making a clean cut just below a leaf node. The node contains high levels of natural auxins, or rooting hormones. Remove all the leaves from the lower half of the stem to prevent them from rotting once inserted into the growing medium.
For enhanced rooting success, dip the cut end into a rooting hormone powder or liquid, such as one containing indole-3-butyric acid (IBA). Insert the prepared cutting about one inch deep into a sterile, well-draining medium, such as a mix of perlite and peat moss or clean sand.
The cuttings require a humid, warm environment with bright, indirect light to successfully initiate roots. Covering the container with a clear plastic dome or bag will maintain the necessary high humidity, but ensure the plastic does not touch the foliage to allow for air circulation. Maintain a temperature range between 65°F and 75°F for optimal cell division and root formation. Roots will typically begin to form within three to five weeks, at which point the plant is ready for the next phase of growth.
Propagation by Division
Division is a faster, simpler method of propagation, relying on the existing root structure of an established plant. This technique is best suited for rejuvenating older chrysanthemum clumps that show reduced vigor and flowering in their centers. Division should be performed in the early spring, just as the new shoots emerge and reach a height of one to three inches.
Carefully dig up the entire plant clump using a garden fork, lifting the root ball intact. Gently shake off excess soil to expose the root system and the crown. The center of an older clump often becomes woody and unproductive; this dead core section should be discarded.
Using a sharp knife or spade, divide the vigorous outer ring of growth into smaller sections, ensuring each new division has several healthy shoots and a substantial mass of fibrous roots. These outer sections are the most productive part of the plant and will quickly establish themselves. Replant the divisions immediately into the garden or pots, providing them with fresh, well-prepared soil.
Essential Aftercare for New Plants
Once cuttings have developed a strong root system or divisions have been replanted, they require careful management for a successful transition to the garden. Rooted cuttings must undergo a process called hardening off, where they are gradually acclimated to outdoor conditions. Begin by placing the young plants in a protected, shaded location outdoors for a few hours each day, slowly increasing their exposure to direct sunlight and wind over a period of three to four days.
Transplant the new plants into their final location in the garden only after the danger of the last spring frost has passed. Plant them at the same depth they were growing previously, taking care not to bury the stem, and firm the soil gently around the root ball. Chrysanthemums thrive in rich, well-draining soil and benefit from initial deep watering to settle the surrounding soil.
Pinching the growth tips encourages a sturdy, full plant structure. When the young plants reach a height of approximately six to eight inches, pinch out the top half-inch of the main stem. This removes apical dominance, stimulating lateral buds to break and creating a bushier plant with multiple flowering stems. Continue pinching until early July to create a more compact and floriferous plant for the autumn season.
Troubleshooting Common Propagation Issues
A common issue encountered during the rooting phase of cuttings is stem rot, which typically manifests as a dark, mushy base on the cutting. This problem is almost always caused by an overly wet or poorly draining rooting medium, which creates an anaerobic environment where fungal pathogens thrive. Ensure the rooting container has ample drainage holes and that the medium remains merely moist, not waterlogged.
Failure to initiate roots can occur if the cutting material was too mature or if the ambient temperature was too low. Using a sterile, porous medium like vermiculite or perlite and maintaining the temperature above 65°F significantly increases the chances of successful root formation. If high humidity is maintained with a plastic cover, make sure to periodically lift the cover to allow for air exchange and prevent the buildup of mold or condensation.
New transplants, whether from divisions or rooted cuttings, may initially wilt, especially if the weather is warm and sunny. This wilting often signals transplant shock or insufficient water uptake in the new location. Providing temporary afternoon shade and ensuring consistent soil moisture for the first few weeks allows the roots time to establish themselves without the stress of excessive water loss through the leaves.