Pinching is an artificial way of forcing plants to branch. The timing of the first pinch on garden mums should be coordinated with growth of the roots and shoot. Before pinching, the plant should have a root system that has reached the bottom and sides of the pot and there should be 1- to 1½-inches of new growth on the cuttings. This generally occurs 12 to 14 days after planting. A soft pinch is used, removing about ½-inch of the stem tip, and allowing 6 to 8 nodes to remain on the cutting. Hard pinches are not desirable because it reduces the number of breaks.
A second or third pinch may be required on some cultivars. These can be applied after 3- to 4-inches of new growth has developed from the previous pinch, again removing ½-inch of growth. Some of the more recent cultivars are heavily self-branching and may not require additional pinches. Regardless, the last pinch should be completed between July 10 and July 25. Late pinches can delay flowering. See Table 3 for a typical pinching schedule.
Garden mum cuttings can, at times, set flower buds prematurely under low temperatures, stress from under watering, low fertilizer levels, late application of the first pinch, or inadvertent exposure to the incorrect photoperiod. Fortunately, they can be developed into quality plants by pinching back further to remove visible buds and unseen developing buds. Cultural practices should also be altered to keep the plant actively growing with plenty of water, fertilizer, light, and space to grow.
Plant growth rate and final height varies among garden mum cultivars. Some growth regulation is beneficial to most cultivars, but is essential for those cultivars that grow too tall for a quality product. A plant growth regulator can be applied after the final pinch when 1- to 2-inches of new growth has occurred. This will reduce final plant height, intensify dark green color of the foliage, and result in a more rounded, uniform product. The most commonly used growth regulator for garden mums is B-Nine. It is applied as a foliar spray at 2500 ppm about 2 weeks after the last pinch. Additional application at the same rate can used if plants begin to stretch, but should not be applied after flower buds are visible. Late application can reduce flower size. See Table 3 for a typical growth regulator schedule.
Garden mums respond to photoperiod or the length of the day (more correctly, the length of the night) to produce flower buds. They are facultative short-day plants which means that they will eventually flower under any day length but flower much faster when the day length is shorter than the night length. The critical day length for the majority of garden mum cultivars is between 13.5 and 14.5 hours. This means that some cultivars initiate flowers earlier in the season while others initiate flowers later.
Garden mum cultivars can be classified by response groups. This refers to the amount of time between the beginning of short-day conditions and flowering. Most garden mum cultivars have a response time between 6 and 9 weeks. Response group and critical day length interacts to determine when a given cultivar will flower. Response time information is only useful under conditions where temperature and photoperiod are carefully controlled such as in a greenhouse. Under outdoor conditions cultivars can be better classified into early, mid and late-season bloomers based on when they initiate flowers and how long they take to flower.
Unfortunately, temperature can modify the photoperiodic response for flowering in garden mums. The critical day length decreases as the night temperature increases above about 72 to 74°F. This means that flower initiation can be delayed when night temperatures are warm at the beginning of short-day conditions and flowering will generally be later in the season. This discussion helps explain why the same garden mum cultivar may bloom later or earlier from one year to the next.
A generalized production schedule for fall production of garden mums is provided in Table 3. This is a basis for planning a schedule, but variations can occur due to cultivar response group, final plant size desired, cultural practices and environmental factors.
Final plant size and container size desired for the market will influence scheduling. Generally, smaller plants in smaller containers require a shorter production schedule (cuttings planted later) and larger plants grown in larger containers require a longer production schedule (cuttings planted earlier). In addition, 10 to 14 days should be added to a schedule if production starts with unrooted cuttings to allow for propagation time.
The number and timing of pinches can also influence production timing. Generally, more pinches will increase production time. The timing of the last pinch is especially critical. Delaying the last pinch will delay flowering, but this response varies by cultivar. Application of the growth retardant, B-Nine, can also delay flowering. The amount of delay depends upon the cultivar, concentration and timing of applications. Late applications, especially after flower initiation can cause significant delay.
When all the factors that may influence garden mum scheduling are considered together, it makes sense for the grower to establish a system of record keeping on the performance of cultivars and cultural practices as an aid to fine tuning future production. This might consist of a notebook with a page for each cultivar, container size, and potting date. Dates would be recorded for all of the major production steps including when the plants were ready for market. Information accumulated over several years can then be used to more precisely plan next year's crops.