How to Manage Temperature and Timing in Garden Mum Production
Flowering chrysanthemums and santinis in a greenhouse in The Netherlands. | Julia700702 via iStock
As Michigan growers are in the full swing of fall garden chrysanthemum production, understanding the complex relationship between temperature, photoperiod, and environmental stressors is essential for producing high-quality, market-ready plants. As summer brings high temperatures across Michigan and throughout most of the U.S., mum growers face challenges in maintaining plant quality and meeting market timelines. Research from Michigan State University Extension highlights how low or high temperatures, especially during the night, can significantly impact mum growth, development, and marketability. Understanding these effects and implementing adaptive strategies can help growers stay on track for fall sales.
Temperature and Photoperiod: A Delicate Balance
Garden mums are short-day plants, meaning they naturally initiate flowering in late July as day lengths begin to shorten. However, temperature plays an equally critical role, especially during the first two weeks of short days, when flower bud initiation is most sensitive. Cool nights (less than about 60°F, depending on the variety) can trigger premature budding, resulting in flowers buried in the canopy and plants that may not meet market standards for height and uniformity.
Strategies to Alleviate Crown Budding
For growers who encounter several consecutive cool nights, steps can be taken to lessen the impact of crown bud formation:
- Immediately pinch off crown buds when possible.
- Supply adequate nutrition. Remember, chrysanthemums are heavy feeders that respond well to fertilizer adjustments. To lessen the impact of crown buds, use a high ammoniacal fertilizer, such as 20-10-20, at up to 300 parts per million (ppm) to promote vegetative growth.
- Plan on applying ethephon (Florel, Collate) early in production. A spray application at a rate of 300-500 ppm is recommended. Spray water pH must be adjusted to 5.0 or lower before adding the ethephon. More information on ethephon applications can be found in the article “Using the PGRs Collate and Florel.”
Heat Stress and Its Impact on Mums
Conversely, high temperatures above 85°F can cause “heat delay,” pushing flowering back by one to three weeks. Uneven flowering, bud deformation, and crown buds, as well as poor branching, reduced growth, and flower color reversion, are also linked to high temperatures during flower initiation and development. These effects are most pronounced during the first two weeks of short days, a critical period for bud initiation. This delay can disrupt planned shipping schedules and reduce the plants’ appeal at retail.
Temperatures between 65-70°F are recommended for the most rapid flower production, although warmer days (but not warmer nights) are usually fine. However, lower temperatures late in production, once flower initiation is complete, can increase flower number and flower size, while having little effect on crop development time. You can read more about the impacts that temperature has on garden mums in this article, “Temperature on Chrysanthemum.”
Mitigating Heat Effects
To counteract the negative effects of high temperatures, several cultural and environmental control strategies can be utilized.
- Adjust Photoperiod for Early-Season Varieties: The shorter the day length, 10-12 hours of light (12-14 hours of darkness), the less chance there is of heat delay.
- Pull Black Cloth in the Early Morning: Pulling black cloth late in the day can trap hot air under and cause excessively warm nights, which can lead to heat delay.
- Optimize Irrigation: Ensure consistent moisture without overwatering, as water stress will further suppress growth.
- Monitor Fertility: High temperatures can alter nutrient uptake, especially if you’re relying on controlled-release fertilizers. Regularly test the substrate electrical conductivity and adjust fertilizer programs to maintain proper nutrition.
For additional information on managing garden mum production, including ways to increase height in compact plants, please read the original article written by Caitlin Splawski and found on the MSU Extension website.
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