Amaryllis (Hippeastrum spp.) is a popular flowering bulb known for its vibrant blooms and relatively easy care. However, temperature plays a critical role in its growth cycle, affecting everything from bulb dormancy to flowering. Understanding the ideal temperature range and tolerance levels is essential for cultivating healthy amaryllis plants.
Amaryllis thrives in moderate temperatures, with the ideal range for active growth being between **65°F to 75°F (18°C to 24°C)**. Within this range, the plant efficiently photosynthesizes, develops strong foliage, and produces robust flower stalks. Temperatures outside this range can slow growth or trigger dormancy prematurely.
Amaryllis exhibits varying temperature tolerances depending on its growth phase:
During dormancy (typically late summer to early autumn), amaryllis prefers cooler temperatures of **50°F to 55°F (10°C to 13°C)**. This period is crucial for bulb rejuvenation. Prolonged exposure to temperatures below **45°F (7°C)** can damage the bulb, while excessive heat may disrupt dormancy.
Once growth resumes, temperatures should gradually increase to the optimal range. Flowering is most prolific at **68°F to 70°F (20°C to 21°C)**. Temperatures above **80°F (27°C)** may cause stress, leading to shorter bloom duration or wilting.
After flowering, foliage development requires stable temperatures of **60°F to 75°F (15°C to 24°C)**. Cooler temperatures slow leaf growth, while excessive heat can cause yellowing or premature die-back.
Amaryllis is sensitive to temperature extremes:
Temperatures below **45°F (7°C)** can cause bulb rot or inhibit flowering. Frost is particularly damaging, often killing foliage and bulbs. In colder climates, amaryllis must be grown indoors or lifted and stored during winter.
Prolonged exposure to temperatures above **85°F (29°C)** can lead to dehydration, stunted growth, or flower abortion. High heat during dormancy may prevent the bulb from entering rest, weakening future blooms.
To maintain ideal conditions:
Keep amaryllis in a room with consistent temperatures, away from drafts or direct heat sources like radiators. Use a thermometer to monitor conditions.
In warm climates (USDA zones 9-11), plant bulbs in partial shade to protect from afternoon heat. In cooler zones, grow in containers and move indoors when temperatures drop below **50°F (10°C)**.
Gradually reduce watering and move the plant to a cooler location (e.g., a basement) for 8-10 weeks to simulate natural dormancy. Avoid freezing temperatures.
Amaryllis tolerates average indoor humidity (40-60%) but benefits from higher humidity in hot conditions. Low humidity combined with high temperatures can cause leaf scorch. Use a pebble tray or humidifier to mitigate dryness.
