Dahlias are popular garden additions, known for their diverse, vibrant blooms. Successful cultivation depends on understanding and managing their temperature requirements.
Optimal Growing Temperatures
Dahlias thrive within a specific air temperature range. Ideal daytime temperatures fall between 65°F and 75°F (18°C and 24°C). This range supports efficient photosynthesis, providing energy for vigorous growth and flower bud formation.
Nighttime temperatures are also important. A slight drop during the night, between 60°F and 65°F (15°C and 18°C), is beneficial. This diurnal fluctuation helps conserve energy and promotes larger, more vibrant blooms, instead of only vegetative growth.
Temperature Considerations for Planting and Establishment
Soil temperature is important for tuber establishment. Plant tubers when soil temperature consistently reaches 60°F (15°C) or above. Planting in cooler soil can lead to tubers rotting before sprouting, as cold, wet conditions are unfavorable for growth.
Conversely, planting too late into excessively warm soil can stress the plant, hindering establishment. Spring air temperatures also influence young dahlia plants. If unexpected cold snaps occur after planting, providing temporary protection, such as cloches or row covers over emerging shoots, can shield them from chilling and frost damage.
Managing Temperature Extremes
Dahlias stress when temperatures deviate significantly from their optimal range. In periods of extreme heat, above 85°F (29°C), dahlias may exhibit signs of stress like wilting, reduced flower production, or smaller blooms. Providing afternoon shade, increasing watering frequency, and applying organic mulch around plant bases can mitigate heat stress by cooling the root zone and reducing moisture loss.
Conversely, dahlias are susceptible to cold temperatures and frost. Temperatures below 50°F (10°C) can slow growth, and a hard frost, around 32°F (0°C) or below, will damage or kill foliage. In late spring or early fall, if unexpected cold snaps are forecast, covering plants with frost cloths or moving potted dahlias indoors overnight protects them from damage.
Temperature for Tuber Storage
Proper temperature management is essential for overwintering dahlia tubers in cold winter regions. The ideal storage temperature for dormant dahlia tubers is between 40°F and 50°F (4°C and 10°C). Maintaining this range prevents tubers from rotting due to excessive warmth and humidity, and deters premature sprouting.
Too-high temperatures encourage sprouting before planting season, while too-low temperatures, especially below freezing, can damage tuber tissue. Humidity levels also interact with temperature; a slightly humid but cool environment prevents desiccation, which can cause tubers to shrivel and dry out. Storing tubers in materials like peat moss or wood shavings in a cool, dark location regulates both temperature and moisture.