Lobelia plants are a popular choice for gardeners due to their vibrant colors and versatile growth habits. Their abundant blooms add continuous color to garden beds, containers, and hanging baskets throughout the growing season.
Understanding Different Lobelia Types
Lobelia encompasses a diverse group of plants, with variations in their life cycles and forms. Many popular varieties are grown as annuals, completing their life cycle within one growing season, though some are technically tender perennials that behave as annuals in cooler climates. Perennial lobelias, such as Lobelia cardinalis (Cardinal Flower) and Lobelia siphilitica (Great Blue Lobelia), return year after year in appropriate hardiness zones.
Lobelia types vary in growth habits. Trailing varieties are often used in hanging baskets and containers. Upright or mounding forms suit garden beds and borders, providing structure. Flowers come in a wide spectrum of colors, including blue, purple, pink, red, and white, with some featuring contrasting ‘eyes’ or markings.
Planting Lobelia
Site Selection
Lobelia thrives in full sun to partial shade, needing at least four to six hours of direct sunlight daily. In regions with intense summer heat, afternoon shade protects plants from stress and prevents flowering from waning. Lobelia is versatile for placements like garden beds, borders, or as edging.
Soil Preparation
Lobelia prefers rich, well-draining, slightly acidic soil, with an ideal pH between 6.0 and 7.0. Incorporating organic matter like compost or well-rotted manure improves soil structure, drainage, and nutrient content. For containers, use a high-quality all-purpose potting mix.
Planting Process
Plant Lobelia after the risk of frost has passed, typically in late May or early June. Loosen the soil and dig a hole slightly wider and deeper than the root ball. Gently remove the plant from its nursery pot, teasing out any pot-bound roots.
Set it in the hole so the top of the root ball is level with the surrounding soil. Backfill, tamp lightly, and water thoroughly. Space plants 6 to 18 inches apart, depending on the variety.
Ongoing Care for Lobelia
Watering
Lobelia requires consistent moisture and does not tolerate drying out. Keep the soil evenly moist but not waterlogged to prevent root rot. During spring and summer, water about once a week, though daily watering may be needed in hot or dry conditions. Check the top inch of soil; if it feels dry, water again.
Fertilizing
Lobelia is considered a heavy feeder and benefits from regular fertilization to support its continuous blooming. Applying a slow-release granular fertilizer at the time of planting provides initial nutrients. This can be supplemented with a liquid all-purpose fertilizer every two to four weeks throughout the growing season. For container-grown plants, a liquid feed formulated for flowering plants, often higher in phosphorus, can promote more abundant blooms.
Pruning and Deadheading
While many annual Lobelia varieties are self-cleaning and naturally drop spent flowers, pruning and deadheading can still be beneficial. Removing faded blooms encourages the plant to put energy into producing new flowers rather than seeds, promoting continuous blooming. If plants become leggy or less vigorous by mid-summer, a light shearing, cutting back stems by up to a third or half, can rejuvenate growth and encourage a fresh flush of blooms. For perennial Lobelias, cutting back old flower stems after blooming and trimming foliage in autumn helps prepare them for winter.
Common Lobelia Issues
Lobelia plants can encounter a few common problems, often related to environmental conditions or pests. Yellowing leaves, a frequent concern, can indicate either overwatering or underwatering, both of which impair the plant’s ability to absorb nutrients. Yellowing might also signal a nutrient deficiency, such as a lack of nitrogen, potassium, or magnesium, or even a pH imbalance in the soil. Adjusting watering practices and ensuring proper soil amendments can often resolve these issues.
Pests like spider mites, aphids, whiteflies, and slugs can affect Lobelia. Spider mites, in particular, can cause browning foliage due to their feeding habits, which can be managed with insecticidal soap or neem oil. Aphids and whiteflies feed on sap, leading to distorted growth and sticky residue. Slugs create irregular holes in leaves, and barriers or manual removal can help control them. Fungal diseases such as root rot, often caused by overwatering, and gray mold (Botrytis cinerea), which thrives in cool, wet conditions, can also impact Lobelia. Ensuring good air circulation and proper drainage helps mitigate the risk of these diseases.