Lobelia trigonocaulis
forest lobelia
eastern Australia (Queensland and New South Wales)
Overview
Lobelia trigonocaulis is a low-growing perennial herb in the family Campanulaceae, reaching 4–8 inches (10–20 cm) tall and spreading 12–24 inches (30–60 cm) wide by rooting at the stem nodes. The stems are three-angled in cross-section, a feature reflected in the species name. Leaves are oval to lance-shaped, 0.4–1.2 inches (1–3 cm) long, with toothed margins and a mid-green upper surface. Flowers are blue to violet with a paler throat, two-lipped, and measure about 0.5 inch (12–15 mm) across, appearing singly on slender stalks from the leaf axils. Bloom occurs mainly from late spring through autumn in its native range. The plant grows in moist, shaded positions along rainforest margins and in wet eucalypt forest in eastern Australia. It tolerates short dry periods once established but thins in prolonged drought and full exposure. As a groundcover it forms a loose mat rather than a dense carpet, leaving gaps where individual stems run. The blue flowers draw native bees and other small pollinators. It spreads steadily in damp soil and can move beyond its intended area in irrigated beds, needing periodic trimming to contain.
Native Range
Lobelia trigonocaulis is native to eastern Australia, occurring in Queensland and New South Wales. It grows along rainforest margins and in moist eucalypt forest, often near streams and in shaded gullies.Suggested Uses
Grown as a groundcover in shaded, moist garden beds and along pond and stream edges. Suited to native and woodland-style plantings in frost-free to light-frost climates. Also grown in containers and hanging baskets where the trailing stems spill over the rim.How to Identify
Appearance
Size & Dimensions
Height4" - 8"
Width/Spread1' - 2'
Bloom Information
Flowering runs from late spring through autumn, roughly November to April in its southern-hemisphere range. Individual flowers are blue to violet with a paler throat and last several days each. Flowering slows during the coolest months and in dry conditions.
Detailed Descriptions
Flower Description
blue to violetFoliage Description
mid-greenGrowing Conditions
Sun Requirements
Requires 2-6 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Grow Lobelia trigonocaulis in part shade to full shade in moist, humus-rich soil that drains freely. Steady moisture supports continuous growth, and the plant wilts and thins during extended dry spells. Soil pH from 5.5 to 7.0 suits it. In frost-prone areas the foliage dies back in winter and regrows from the base in spring. A light organic mulch helps retain soil moisture and keeps the roots cool. Trim runners once or twice a year to hold the mat within bounds.Pruning
Trim spreading stems once or twice during the growing season to keep the plant within its space. Remove spent flower stalks to tidy the clump. No structural pruning is needed for this low herb.Pruning Schedule
J
F
M
A
M
J
J
A
S
O
N
D
late springsummer
Container Growing
✓ Suitable for container growing
Minimum container size: 1 gallons