When to plant Lobelia in Subtropical Australia
Subtropical zone — applies to Brisbane, Gold Coast, Sunshine Coast, Coffs Harbour, Lismore and similar areas. Growing elsewhere? Temperate · Cool · Tropical · Arid.
Raise lobelia seedlings from February to May, sowing the dust-fine seed barely 1 mm deep and transplanting once the plants are large enough to handle. In subtropical areas like the Sunshine Coast and Lismore, an autumn start suits this half-hardy flower, letting it grow through the mild winter for a long cool-season display. Seed germinates in 14–21 days and needs light to sprout, so press it onto the surface rather than burying it. Space transplants 15 cm apart with rows 15–20 cm apart. At 100–120 days to maturity, lobelia rewards early sowing with mounds or trailing sprays of blue, mauve and white.
Sowing calendar — subtropical zone
Green months are your sowing window: February to May.
Growing notes
Lobelia is best treated as a cool-season flower in the subtropics. It grows and blooms happily through the mild frost-free winters of Brisbane and the Gold Coast, then fades once summer heat and humidity arrive. Sowing in autumn gives you the longest run of colour before the wet season shuts it down.
The seed is extremely fine, which is where most people come unstuck. Sow into a punnet of fine, moist mix, do not cover it, and mist gently rather than watering with a can that will wash it away. Keep the surface consistently damp and bright until germination, then prick out clumps rather than single seedlings once they are big enough to lift.
The main failure mode here is heat and humidity stress: plants go leggy, stop flowering and rot at the crown when the muggy weather sets in. Head this off by keeping lobelia in a spot with morning sun and some afternoon shade, watering at the base, and trimming plants back lightly after the first flush to encourage a second wave. Good airflow between plants reduces the fungal problems that thrive in coastal humidity.
Lobelia at a glance
| Sowing depth | 1 mm |
|---|---|
| Plant spacing | 15 cm |
| Row spacing | 15-20 cm |
| Germination | 14-21 days |
| Days to maturity | 100-120 days |
| Frost tolerance | Half Hardy |
| Method | Plant Seedlings |
Common questions
- can you grow lobelia in Brisbane
- Yes, as a cool-season flower. Sow from February to May and grow it through the mild winter, when Brisbane's frost-free conditions suit it best. It struggles once summer heat and humidity return.
- why is my lobelia seed not germinating
- Lobelia seed needs light to sprout and is easily buried or washed away. Sow it on the surface at about 1 mm, do not cover it, mist rather than pour, and keep it bright and damp for the full 14–21 days.
- how do you keep lobelia flowering
- Trim plants back lightly after the first flush and water at the base to keep the crown dry. In the subtropics, a shadier position and good airflow help it hold on longer before summer humidity ends the display.
- should I sow lobelia direct or raise seedlings
- Raise seedlings and transplant. The seed is too fine and slow to sow reliably direct into the garden, so start it in punnets and prick out clumps once they are big enough to handle.
Track lobelia in your garden — sow dates, harvest countdowns, reminders. Free.
Add to my garden