From a botanical perspective, the answer to whether you can grow Lobelia as a perennial indoors is complex and hinges on understanding its fundamental life cycle. Most popular garden Lobelias, such as Lobelia erinus (edging lobelia), are classified as tender perennials. This means their genetic programming is for a perennial life cycle, but they lack frost tolerance. In their native habitats or in USDA zones 10-11, they survive year-round outdoors. However, when brought indoors, they escape the killing frost, fulfilling the primary condition to behave as a true perennial. The plant's physiology does not receive the environmental signal to die back completely, allowing it to potentially persist for multiple years.
For a Lobelia plant to transition successfully to an indoor perennial, its specific environmental needs must be met meticulously. Light is the most critical factor. Lobelias are high-light plants, requiring several hours of direct sunlight daily to thrive and, most importantly, to bloom. A south-facing window is ideal. Without sufficient light, the plant will become leggy, etiolated, and cease flowering as it stretches for a light source. Temperature is another key factor. They prefer cooler conditions, ideally between 60-70°F (15-21°C). A consistently warm and dry environment, common in many homes during winter, can stress the plant and encourage pest infestations like spider mites.
Sustaining Lobelia as a perennial requires attentive cultural practices. Well-draining soil is non-negotiable; a standard potting mix with added perlite is suitable to prevent waterlogged roots, which the plant is highly susceptible to. Watering must be consistent—keeping the soil evenly moist but never soggy. The plant will indicate stress by wilting dramatically if too dry. Furthermore, to encourage a perennial habit, diligent deadheading (removing spent flowers) is essential. This practice redirects the plant's energy from seed production back into vegetative growth and new flower bud formation, extending its lifespan and blooming period indoors.
A significant physiological challenge with maintaining Lobelia indoors is its natural tendency to become woody and leggy at the base over time, even under good conditions. This is a normal part of its growth habit. To combat this and truly grow it as a perennial, aggressive pruning is required. After a flush of blooms or if the plant becomes straggly, cut it back by one-half to two-thirds. This severe pruning shocks the plant into producing new, bushier growth from the base, effectively renewing it. Without this intervention, the plant will likely look unsightly and decline in vigor, making it more of a short-term occupant rather than a long-term perennial specimen.
From the plant's viewpoint, the most reliable way to achieve "perennial" Lobelia indoors is not necessarily by sustaining the original mother plant indefinitely, but by using the original plant to create new generations. Lobelia roots readily from stem cuttings. Taking 3-4 inch cuttings, removing the lower leaves, and placing them in water or a moist potting mix will create genetic clones of your original plant. This method bypasses the issues of woodiness and decline. By perpetually propagating new plants from cuttings every few months, you can maintain a continuous, vibrant presence of Lobelia in your indoor space, effectively mimicking a perennial collection.
