Geraniums are a popular choice for gardens and containers due to their vibrant blooms and relative ease of care. These flowering plants, often referred to as Pelargoniums, bring a splash of color to outdoor spaces throughout the warmer months. Understanding their temperature requirements is important for ensuring their health and maximizing their flowering potential, as they are sensitive to temperature extremes.
Optimal Growing Temperatures
Geraniums thrive within a specific temperature range. For optimal performance, daytime temperatures between 70°F and 85°F are ideal, and nighttime temperatures should remain between 55°F and 65°F. Maintaining these conditions supports efficient photosynthesis and metabolic processes. Temperatures outside this range can hinder the plant’s ability to flourish.
Protecting Geraniums from Cold
Geraniums are not tolerant of freezing temperatures and are grown as annuals in regions with cold winters. Temperatures below 50°F can cause cold damage, and growth slows. Freezing temperatures, particularly below 28°F, can cause permanent damage or kill the plant. Bring potted geraniums indoors before the first hard frost, ideally when nighttime temperatures consistently drop below 45°F.
For container plants, move them to a protected indoor location like a sunroom or cool basement. If kept as houseplants, ensure they receive bright light and maintain indoor temperatures around 60-65°F during the day and 50-60°F at night. Another method involves preparing plants for dormancy:
- Dig them up before a hard freeze.
- Gently shake off excess soil.
- Store them in a cool, dry place around 50-60°F, such as a garage or basement.
- Hang them upside down or place them in unsealed paper bags or cardboard boxes to facilitate this dormant state.
Protecting Geraniums from Heat
Prolonged exposure to high temperatures can also negatively impact geraniums, leading to reduced growth and flowering. Temperatures consistently above 85°F can cause heat stress, resulting in symptoms like bleached or chlorotic foliage. In climates where temperatures exceed 100°F, geraniums may struggle even in full sun. Providing afternoon shade is beneficial, particularly during the hottest parts of the day.
Increase watering frequency during heat waves, but avoid overwatering, which can lead to root rot. Water deeply in the morning or evening to minimize evaporation and allow the plant to absorb moisture effectively. Ensuring good air circulation around plants, especially in containers, helps dissipate heat. Using light-colored pots can also help keep the root zone cooler than darker containers.
Recognizing Temperature Stress
Observing your geraniums for visual cues can help diagnose temperature-related issues. Cold stress symptoms include:
- Wilting leaves.
- Marginal leaf graying.
- Necrosis.
- Blackening of foliage.
Chilling injury, occurring at temperatures below optimal but above freezing, can manifest as leaf whitening or rolling.
Signs of heat stress include:
- Yellowing leaves.
- Wilting even with adequate watering.
- Stunted growth.
- A reduction in flowering.
Foliage may also appear bleached or chlorotic, particularly on young leaves. If these symptoms appear, the plant is struggling and requires intervention.
Seasonal Temperature Management
Effective temperature management for geraniums involves adapting care practices throughout the year. In spring, wait until all danger of night frost has passed and nighttime temperatures are consistently above 55°F before moving plants outdoors. This occurs after mid-May in many regions. Gradually acclimate plants to outdoor conditions by exposing them to increasing periods of sunlight and outdoor temperatures over several days.
During summer, monitor temperatures and provide shade during peak heat. Water thoroughly when the top inch of soil is dry, adjusting frequency based on weather conditions. As autumn approaches, begin preparing outdoor geraniums for cooler temperatures. Reduce watering as growth slows and bring potted plants indoors or prepare them for dormant storage before the first frost.