Annual
Lobelia
Lobelia erinus · Campanulaceae
Also called: Edging Lobelia, Trailing Lobelia, Garden Lobelia
Lobelia (Lobelia erinus) is a moderate-water annual well suited to Tucson and the low desert. It's a moderate-growing annual.
Lobelia at a glance
- Water use
- Moderate (established)
- Sun
- Full sun in the cool months; provide afternoon/filtered shade as spring warms to prolong bloom.
- Mature size
- 4-9 in tall; trailing types spill 10-18 in
- Growth rate
- Moderate
- Bloom
- Blue, violet, purple, white, and rose-pink shades, Winter into spring (roughly Dec-April/May) in the low desert
- Cold hardiness
- Frost-sensitive to tender; damaged by hard freezes (below ~28-30 F) and quickly fades once daytime temps exceed ~85 F.
- Soil
- Rich, well-drained soil amended with compost; consistent moisture and good drainage are key.
- Native range
- South Africa
- Best used as
- Edging, Containers and hanging baskets, Window boxes, Massed winter color, Spiller in mixed pots
- Wildlife
- Flowers attract bees, butterflies, and hummingbirds.
- Toxicity
- Lobelia species contain alkaloids (lobeline) and are considered potentially toxic if ingested in quantity; keep away from curious pets and young children, though casual contact is not a concern.
How to grow Lobelia in Tucson & the low desert
Watering
Keep soil evenly moist; lobelia is not drought tolerant and wilts quickly if it dries out, so water every 2-4 days (more in containers). Grown as a cool-season annual in Tucson: set out transplants Sept 15-Dec.
Fertilizer & nutrients
Feed every 2-3 weeks with a dilute balanced liquid fertilizer; container plants benefit from a slow-release granular at planting plus regular light feeding for continuous bloom.
Pruning & care
Shear back lightly by about one-third if plants get leggy or stop blooming to force a fresh flush; deadheading is generally not required.
Notes
Excellent for trailing winter color in Tucson containers and baskets; pair with calendula, pansy, and alyssum. Plant in fall once nights cool; it is one of the first cool-season annuals to fade in spring heat, so enjoy it Dec-April.
Sources: University of Arizona Cooperative Extension / Pima County Master Gardeners cool-season annual recommendations; Tucson low-desert planting calendars (greenthingsaz.com, growinginthegarden.com); Missouri Botanical Garden Plant Finder