Chrysanthemums, often simply called mums, are celebrated for their vibrant blooms that signal the transition from summer to autumn. To keep these garden favorites thriving, understanding what temperature can mums tolerate is essential. These resilient plants possess a specific thermal range, and staying within it is the primary factor in ensuring healthy growth and a spectacular floral display.
Optimal Growing Temperatures for Mums
For robust development and abundant flowering, mums prefer daytime temperatures between 70°F and 75°F (21°C to 24°C). During the cooler nighttime hours, a range of 60°F to 65°F (15°C to 18°C) is ideal. These conditions mimic their native woodland edge environments, promoting sturdy stems and lush foliage. Temperatures consistently above 85°F (29°C) can cause stress, leading to leggy growth and bud drop, while sudden cold snaps can damage tender new growth.
Tolerance to Cold Temperatures
Mums are generally hardy perennials in cooler climates, but their cold tolerance depends heavily on the stage of growth. Established plants in the garden can typically survive temperatures down to 20°F (-6°C) once they have hardened off. However, young plants or those in containers are far more susceptible to frost damage. Protecting them with a layer of mulch around the base or moving potted specimens indoors can prevent winter kill.
Cold Hardiness by Variety
Garden Hardy Mums: These varieties are bred specifically for outdoor cultivation and can tolerate freezing temperatures.
Pot Mums: Bred for containers, they have less cold resistance and often require relocation to a sheltered spot during winter.
Florist Mums: Primarily grown as indoor annuals, they have minimal cold tolerance and thrive only in controlled, warm environments.
Managing Heat and Summer Stress
While mums are associated with cool autumn weather, they struggle in the intense heat of high summer. Prolonged exposure to temperatures over 90°F (32°C) can cause significant problems, including wilted leaves and faded colors. To combat this, plant mums in a location that receives morning sun and afternoon shade. Consistent watering is critical during heatwaves to keep the soil moist but not waterlogged, which helps the plant regulate its temperature.
The Critical Role of Temperature in Blooming
The temperature tolerance of mums directly dictates their blooming cycle. These short-day plants require long nights to initiate flower buds. If nighttime temperatures remain too warm, usually above 60°F (15°C), the plant may fail to bloom altogether. Conversely, a period of cool nights (around 50°F to 55°F or 10°C to 13°C) encourages the formation of dense, colorful flower clusters, making temperature management vital for the aesthetic appeal of the plant.
Transitioning Mums Between Environments
Whether moving mums from a greenhouse to the garden or from outdoors to a sunny kitchen, sudden temperature changes can lead to shock. Gradual acclimatization, known as hardening off, is necessary. Start by placing the plants in a shaded, protected area for a few hours each day, slowly increasing their exposure to direct sun and outdoor temperatures over the course of one to two weeks. This process strengthens the plant and prepares it to handle what temperature fluctuations it will face outside.
Winter Protection Strategies
In regions with harsh winters, protecting mums ensures they survive to bloom again. Mulching is the most effective method; a 4-inch layer of straw or shredded leaves around the base insulates the roots against freezing temperatures. For container-grown mums, grouping them together and moving them to an unheated garage or basement reduces their exposure to drying winds and extreme cold. Avoid watering dormant plants during winter, as excess moisture can lead to root rot.
