Snapdragons (Antirrhinum majus) are cherished garden flowers, celebrated for their vibrant, spiked blooms that bring vertical interest and a wide array of colors to any landscape. Their unique flower shape resembles a dragon’s snout. While versatile, snapdragons are sensitive to temperature extremes. Understanding their temperature preferences is important for cultivating healthy plants and ensuring abundant flowering.
Optimal Growing Temperatures for Snapdragons
Snapdragons flourish in cooler conditions, making them a favored choice for spring and fall gardens. For optimal growth and prolific flowering, they prefer daytime temperatures in the low 70s Fahrenheit (21-24°C) and nighttime temperatures in the low 40s Fahrenheit (4-7°C). This explains why they are often grown as annuals in many regions, providing color during milder months.
When starting snapdragons from seed, specific temperatures aid germination. Seeds sprout best when soil temperatures are consistently between 70-75°F (21-24°C). After germination, young seedlings thrive in slightly cooler conditions, ideally 65-75°F (18-24°C) during the day, with slightly cooler nights. These conditions support robust vegetative growth, leading to strong stems and abundant blooms.
Snapdragons and Cold Weather
Snapdragons exhibit notable cold tolerance, often classified as hardy in USDA zones 7-11, and can be overwintered in zones as low as 5 with proper protection. Established plants withstand sub-freezing temperatures and tolerate light frosts, allowing planting a couple of weeks before the last expected spring frost. They can survive temperatures down to 14°F (-10°C) with cover, and seedlings endure -5°C (23°F).
Despite their cold hardiness, prolonged exposure to severe freezing conditions can impact survival. To protect snapdragons from intense cold, apply a layer of mulch, such as pine straw or leaf mulch, around the plant base to insulate the root zone. For container-grown snapdragons in colder climates, move them indoors to a cool, dark, frost-free location like a garage or basement to overwinter in a dormant state. In milder zones, these plants may self-seed or return from the original plant in spring after foliage dies back.
Snapdragons and Hot Weather
Snapdragons are cool-season flowers and struggle with prolonged high temperatures, often slowing or stopping blooming entirely during mid-summer heat. Excessive heat can lead to reduced flowering, wilting, and leggy growth as plants stretch for cooler air. In very hot climates, snapdragons may enter dormancy, where growth and blooming cease until cooler weather returns.
To help snapdragons cope with heat, provide afternoon shade, especially in regions with intense summer sun. Adequate, consistent watering is important to mitigate heat stress; deep watering two to three times per week is recommended during hot spells. Apply a 2-3 inch layer of organic mulch to keep soil and roots cooler by conserving moisture and moderating soil temperature. Some newer snapdragon varieties, such as ‘Snappy’, ‘Snapshot’, ‘Rocket’, ‘Twinny’, and ‘Liberty’ series, have been bred for improved heat tolerance, extending their bloom period into warmer months.
Recognizing and Addressing Temperature Stress
Identifying signs of temperature stress in snapdragons allows for timely intervention. In cold conditions, cues include stunted growth or purplish discoloration of leaves, particularly if exposed to temperatures below 40°F (4°C) for extended periods. If frost damage occurs, leaves may appear water-soaked, then turn black or brown. For cold-stressed plants, ensure they are well-watered and protected with mulch; extremely damaged plants may need to be cut back to encourage new growth in warmer weather.
Conversely, heat stress manifests as wilting, even when soil moisture seems adequate, or leaf scorch, where leaf edges turn brown and crispy. Blooms may drop prematurely, and the plant’s overall vigor can decline, sometimes entering dormancy. To address heat stress, increase watering frequency, especially deep watering in the morning. Provide temporary shade with shade cloth or relocate container plants to a shadier spot to reduce direct sun exposure. If plants are severely affected, a mid-season cutback can encourage new growth and blooms once cooler temperatures return.