Geraniums (Pelargonium spp.) thrive in moderate daytime temperatures, ideally between 65°F to 75°F (18°C to 24°C). This range supports robust photosynthesis, ensuring healthy growth and vibrant blooms. Temperatures above 85°F (29°C) can stress the plant, leading to wilting or reduced flowering, while prolonged exposure to temperatures below 50°F (10°C) may stunt growth.
At night, geraniums prefer slightly cooler conditions, ideally 55°F to 60°F (13°C to 16°C). This drop mimics their natural habitat and promotes cellular recovery. Consistently warm nights (above 70°F/21°C) can weaken the plant over time, while temperatures below 40°F (4°C) risk frost damage or dormancy.
Geraniums are resilient but have clear limits. They can briefly tolerate temperatures up to 90°F (32°C) if shaded and watered adequately. Conversely, they survive light frosts (down to 30°F/-1°C) but may lose leaves. Prolonged freezing temperatures (<28°F/-2°C) are usually fatal.
For outdoor geraniums, spring and fall are ideal, while summer may require partial shade. In winter, move potted geraniums indoors to a cool (45°F–50°F/7°C–10°C), bright location to induce dormancy. Indoor geraniums year-round need stable temperatures near 70°F (21°C) with good airflow to prevent legginess.
Root health depends on soil temperature. Aim for 60°F–70°F (15°C–21°C) in the root zone. Cold, wet soil (<50°F/10°C) invites root rot. Mulching helps regulate soil temperature outdoors. Avoid placing indoor pots near cold drafts or heat vents, which create uneven air temperatures.
Consistent warmth (65°F–75°F/18°C–24°C) maximizes blooming. High heat (above 80°F/27°C) may reduce flower production, while cool nights (<50°F/10°C) slow bud formation. For overwintered plants, gradual reintroduction to warmer spring temperatures encourages prolific blooms.
In hot climates, plant geraniums in dappled shade and water deeply. In cooler regions, use south-facing walls or containers to retain heat. Greenhouses should maintain 60°F–75°F (15°C–24°C) with ventilation to prevent overheating.
Yellowing leaves indicate heat stress or cold shock. Drooping stems suggest overheating, while red-tinted foliage signals cold exposure. Adjust placement or insulation accordingly to restore ideal conditions.
