From a botanical perspective, the ideal pot begins with an understanding of the plant's root architecture. Lobelia species, particularly the popular annual bedding types (Lobelia erinus), possess a relatively fine and fibrous root system. They are not deep-rooting plants like tomatoes or trees. Instead, their roots tend to spread laterally in the top few inches of soil. This characteristic immediately suggests that a pot that is excessively deep is unnecessary and can even be detrimental. Deep containers hold more soil volume, which retains water for longer. For Lobelia's delicate roots, which prefer consistent moisture but abhor being waterlogged, a pot that is too deep increases the risk of root rot in the lower, saturated soil layers that the roots may never even reach.
Selecting the correct pot size is a balance between providing enough room for growth and avoiding the pitfalls of excess soil. For most Lobelia plants, a pot with a diameter of 6 to 8 inches is ideal. This size comfortably accommodates the root spread of a single plant or a small cluster. When planting multiple Lobelias for a full, cascading effect, a larger container—such as a 10 to 12-inch window box or hanging basket—is appropriate. The key is to ensure there is adequate space for air circulation between the stems to prevent fungal diseases. A pot that is too small will cause the plant to become root-bound too quickly, leading to stress, nutrient deficiency, and a need for constant watering. Conversely, a pot that is too large will hold excessive moisture around the roots, creating an anaerobic environment that suffocates the roots and fosters pathogens.
The material of the pot significantly influences soil moisture and temperature, two factors critical to Lobelia health. The primary choices are porous materials like terracotta/clay and non-porous materials like plastic, glazed ceramic, or resin.
Porous Pots (Terracotta/Clay): These pots are excellent for Lobelia because they allow air and water to pass through their walls. This "breathing" action helps to prevent overwatering by wicking away excess moisture from the soil, promoting a healthy oxygen flow to the roots. However, this also means the soil will dry out more quickly, requiring more frequent watering, especially in hot, sunny conditions. Terracotta also provides some insulation against heat.
Non-Porous Pots (Plastic, Glazed Ceramic): These materials retain moisture much more effectively, reducing watering frequency. This can be beneficial if you tend to underwater plants. The risk, however, is overwatering. Excellent drainage becomes even more critical with non-porous pots. Plastic pots can also heat up quickly in direct sun, potentially stressing the roots, whereas thicker glazed ceramic pots offer better insulation.
Regardless of the size or material you choose, a pot must have adequate drainage holes. This is an absolute requirement for Lobelia. Without an escape route, water accumulates at the bottom of the pot, creating a stagnant, oxygen-deprived environment. Root rot, caused by fungi like Pythium and Phytophthora, is almost inevitable in such conditions. When selecting a pot, ensure it has at least one substantial hole. For larger containers, multiple holes are preferable. If you find a decorative pot without drainage, it is best to use it as a cachepot (an outer decorative holder) by placing the Lobelia in a plain plastic nursery pot with holes inside the decorative one, ensuring you empty any accumulated water after watering.
