Lobelia, in its many cultivated forms (such as Lobelia erinus), is predominantly grown as a tender perennial or annual. Its genetic predisposition is for mild, cool to warm conditions, but it is not a cold-hardy plant. Most popular indoor varieties thrive in daytime temperatures between 65°F and 75°F (18°C - 24°C). While they can tolerate a slight dip at night, a consistent environment is key. Their metabolism, rate of transpiration, and overall physiological processes are optimized within this range. A cold draft introduces a sudden and stressful variable that falls well outside this ideal spectrum, disrupting these essential functions.
Cold drafts act as a severe stressor on Lobelia plants. When exposed to a direct stream of cold air, several detrimental processes occur. Firstly, the rapid temperature drop causes the plant's cells to cool down too quickly. This can damage cell membranes, reducing their fluidity and compromising their integrity, much like how skin can get frostbite. Secondly, the plant's rate of transpiration (water loss through leaves) can become erratic. The dry, cold air accelerates moisture loss from the leaf surfaces, but the chilled roots in the soil are less efficient at absorbing water to replace it. This creates a water deficit, leading to wilting, leaf curl, and browning edges, even if the soil is adequately moist.
A Lobelia plant suffering from exposure to cold drafts will display clear visual distress signals. The most immediate sign is often wilting, which can be misleading as it mimics underwatering. Closer inspection will reveal leaf edges and tender new growth turning brown or black. The leaves may become soft and mushy in texture rather than dry and crispy, which is more indicative of underwatering or heat stress. Prolonged exposure will lead to significant leaf drop, as the plant sacrifices its foliage to preserve its core. In severe cases, the cold damage will extend to the stems and root system, ultimately killing the plant.
To ensure the health of an indoor Lobelia, it is crucial to place it in a location completely free from cold drafts. This requires careful consideration of the microclimates within a home. Windows, while providing essential light, are common sources of drafts. Check for air leaks around the window frames and ensure the plant is not situated where it would be in the direct path of air flowing from an opened window, especially during colder months. Similarly, keep the plant away from exterior doors that are frequently opened and from the direct blast of air conditioning vents, which can create a similarly stressful cold, dry airflow. A stable, consistently temperate spot with bright, indirect light is the ideal placement.
