To understand the ideal conditions for an Osteospermum, one must first consider its origins. As a native of South Africa, this plant is evolutionarily adapted to a specific set of environmental conditions characterized by warm, sunny days and cooler nights, with moderate humidity and well-draining soils. Our goal as caretakers is to replicate these conditions as closely as possible within the home environment to ensure the plant not only survives but thrives, producing its characteristic daisy-like flowers abundantly.
Temperature is a critical factor for metabolic processes like photosynthesis and respiration. Osteospermum performs best in a daytime temperature range between 65°F and 75°F (18°C - 24°C). This range provides the sufficient warmth needed for robust growth and flower development without causing excessive heat stress. Crucially, these plants greatly benefit from a nighttime drop in temperature. An ideal nighttime range is between 50°F and 60°F (10°C - 15°C). This diurnal temperature variation mimics their natural habitat and is a key trigger for initiating and prolonging the flowering period. Consistently high temperatures, especially at night, can lead to reduced blooming and leggy growth as the plant stretches for cooler air.
From the plant's perspective, humidity directly influences the rate of transpiration—the process of water movement through the plant and evaporation from its leaves. Osteospermum prefers a moderate humidity level, typically between 40% and 60%. In this range, the stomata on the leaf surfaces can open efficiently to facilitate gas exchange for photosynthesis without risking excessive water loss. Humidity levels consistently below 40% can cause the leaf edges to brown and crisp as the plant loses water faster than its roots can absorb it. Conversely, humidity levels consistently above 70% create a stagnant environment that significantly increases the risk of fungal diseases like powdery mildew and botrytis, as well as root rot, as the soil medium will struggle to dry out appropriately.
These environmental factors do not act in isolation. The ideal temperature and humidity must be considered alongside light exposure and watering practices. A plant placed in a very sunny, south-facing window will experience higher localized temperatures and faster soil drying, potentially requiring more frequent watering. In this scenario, maintaining adequate humidity helps the plant cope with the higher transpirational demand. Conversely, a plant in cooler, lower-light conditions will use water much more slowly. Watering must be adjusted accordingly—allowing the top inch of soil to dry out between waterings—to prevent root rot, especially if cooler temperatures and higher humidity are present.
The plant will communicate its discomfort. Symptoms of excessive heat and low humidity include wilting (even when soil is moist), drooping leaves, flower buds that fail to open or drop prematurely, and stunted growth. Signs of excessive cold include blackening or mushiness of leaves and stems. Symptoms of excessive humidity are most often visible as fungal growth: white, powdery residue on leaves and stems (powdery mildew) or gray, fuzzy mold (botrytis). Recognizing these signs allows for timely adjustments to the plant's placement or the room's environment.
