When to plant Lobelia in Temperate Australia
Temperate zone — applies to Sydney, Melbourne, Adelaide, Perth, Newcastle and similar areas. Growing elsewhere? Cool · Subtropical · Tropical · Arid.
Raise lobelia as seedlings from February to May, sowing the dust-fine seed barely 1 mm deep and transplanting once plants are large enough to handle. In temperate gardens this timing suits the mild autumn and cool winter, with seed germinating in 14–21 days and flowering plants ready in around 100–120 days. Space the small mounds or trailers about 15 cm apart, with rows 15–20 cm apart, to knit into a solid edge or basket. Melbourne, Adelaide and Newcastle gardeners get long, generous displays of blue, white or violet from a plant that quietly threads itself through borders, pots and hanging baskets.
Sowing calendar — temperate zone
Green months are your sowing window: February to May.
Growing notes
Lobelia is fiddly at the seedling stage and easy thereafter. The seed is almost invisible, so sow it onto the surface of a fine, moist mix and press it in rather than burying it; that 1 mm depth in the data really means "barely covered". Keep the tray warm and never let it dry out through the 14–21 day germination window.
The classic failure in temperate zones is a mid-summer collapse. Lobelia loves the cool, and a hot, dry Adelaide or Perth summer can brown off the whole plant almost overnight. The fix is a shear-back: cut the plant by a third, give it a good drink and a light feed, and it will usually reflush in the cooler evenings of late summer.
Grow it in morning sun with afternoon shade in warmer temperate spots, or full sun in cooler Melbourne gardens. Consistent moisture is the theme throughout, so mulch beds and check baskets daily in warm weather. A weak liquid feed every few weeks keeps the colour coming. Because it stays low and spreads to about 15 cm, lobelia is ideal for edging paths, softening pot rims and underplanting taller flowers, where its haze of tiny flowers fills every gap.
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
- How do I grow lobelia from seed?
- Sow the very fine seed on the surface of a moist seed-raising mix and barely cover it, no more than 1 mm. Keep it warm and evenly damp until it germinates in 14–21 days, then prick out small clumps and grow on before transplanting at about 15 cm spacing.
- Why did my lobelia stop flowering in summer?
- Lobelia dislikes heat and often stalls or browns off in a hot temperate summer. Shear it back by about a third, water well and feed lightly, and it will usually reflush as the weather cools in late summer and autumn.
- Is lobelia good for hanging baskets in Melbourne?
- Yes, trailing lobelia is one of the best basket fillers for Melbourne's mild climate. Keep the basket consistently moist and give it morning sun, and it will spill over the edge with colour for months.
- How far apart should I plant lobelia?
- Space plants about 15 cm apart with rows 15–20 cm apart. This lets the small mounds knit together into a continuous edge or carpet without crowding each other out.
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