Lobelias prefer cool temperatures but can grow in full sunlight in areas where summer temperatures are mild. Full sun beds may require additional watering as they are prone to drying out more quickly. Mulch over the bed to help keep the roots cool in high sun locations. A 2-inch mulch layer also prevents the soil from drying out too quickly, which helps the lobelia grow lush in the higher light conditions.
Most lobelia are grown in beds that receive some shade, especially in areas with hot, dry summers. Lobelia will not flower in full shade, so choose beds that receive full morning sunlight and afternoon shade when possible. The sunlight at midday is usually warmest, so it's beneficial to choose beds that are shaded at this time. You can also grow lobelia in beds that receive lightly dappled sunlight as long as there are no periods of heavy shade in the bed during the day.
Sunlight and Flowering
Lobelias flower best when provided with some daily sunlight, but too much sun can inhibit blooming during the hottest days of summer. As long as you keep the plants watered, flowering usually resumes as the temperatures begin to cool in late summer or early fall. Lobelia primarily flowers in spring and fall when sunlight is bright but temperatures are cool.
Potted Plant Light Concerns
Potted plants should be placed in areas protected from midday sun. Container-grown lobelia are more prone to heat stress because the soil in containers dries out more quickly than garden beds. Avoid setting pots or hanging baskets of lobelia in areas that receive full midday sun. In brightly lit locations the containers may require daily watering to prevent the soil from drying out too quickly.