Carnations (Dianthus caryophyllus) are prized for their vibrant, ruffled blooms and clove-like scent. To cultivate robust and floriferous plants, understanding their ideal temperature requirements from a physiological perspective is paramount. Temperature directly influences metabolic rates, photosynthesis, respiration, and developmental processes like flowering.
For optimal vegetative growth—the development of strong stems and lush, green foliage—carnations thrive in a moderately cool temperature range. The ideal daytime temperature for this phase is between **18°C and 24°C (64°F and 75°F)**. Within this range, the plant's photosynthetic enzymes operate at peak efficiency, converting light into energy without excessive stress. Nighttime temperatures should ideally drop to a range of **10°C to 15°C (50°F to 59°F)**. This day-night differential, known as a DIF, is crucial. Cooler nights reduce respiration rates, allowing the plant to conserve the energy produced during the day for growth rather than burning it off. It also promotes stronger, less leggy stems, creating a more compact and sturdy plant structure.
The transition from vegetative growth to flowering (photoperiodism and thermoperiodism) is highly temperature-sensitive in carnations. While they are often classified as day-neutral plants, cooler temperatures significantly enhance flower initiation and quality. The ideal temperature for promoting the development of abundant, high-quality flower buds is slightly cooler than for vegetative growth, typically between **13°C and 16°C (55°F and 61°F)**. Sustained exposure to temperatures within this range encourages the plant to shift its energy from leaf production to the formation of strong, numerous flower scapes. Excessively high temperatures during this phase, especially above 26°C (79°F), can lead to heat stress, inhibiting bud formation or causing bud abortion, where the plant abandons developing buds to conserve resources.
A plant's environment is not limited to the air; the root zone temperature is equally vital. Carnations prefer their roots to be in a stable, cool environment. Ideal soil temperatures mirror the cool nighttime air preferences, ranging from **15°C to 18°C (59°F to 64°F)**. Warm soil temperatures can severely hamper root function, reducing the uptake of water and essential nutrients like phosphorus. This can manifest as stunted growth, wilting despite adequate soil moisture, and nutrient deficiencies. Maintaining a cool root run, often achieved through light-colored mulch or appropriate container selection, is a key factor in overall plant health and stress resilience.
Carnations are resilient but have distinct limits. Prolonged exposure to temperatures **below 10°C (50°F)** dramatically slows metabolic activity, halting growth and delaying flowering. A hard frost can damage tender new growth and flower buds. Conversely, temperatures consistently **above 27°C (80°F)** induce significant heat stress. The plant's transpiration rate skyrockets in an attempt to cool itself, potentially leading to water stress and wilting. High heat also increases photorespiration, a process that wastes energy and reduces net photosynthesis, weakening the plant. This results in shorter stems, smaller flowers, reduced fragrance, and a general decline in vitality, making the plant more susceptible to pests like spider mites that thrive in hot, dry conditions.
