When to plant Larkspur in Subtropical Australia

Subtropical zone — applies to Brisbane, Gold Coast, Sunshine Coast, Coffs Harbour, Lismore and similar areas. Growing elsewhere? Temperate · Cool · Tropical · Arid.

Sow larkspur direct from April to June, scattering the fine seed and barely covering it at just 3 mm deep. Germination takes 10–21 days and is helped by the cool soil of early winter, which the seed needs to break dormancy. This is a long-season annual, maturing in around 140 days, so an autumn sowing sets you up for tall spires of bloom by late spring. Thin plants to 30–40 cm apart in rows 30–40 cm wide. In Brisbane and Gold Coast gardens the narrow autumn window matters, as larkspur resents warm soil at sowing and will not germinate reliably later in the year.

Sowing calendar — subtropical zone

Green months are your sowing window: April to June.

Growing notes

Larkspur is a cool-season annual that gives you the delphinium look from a direct-sown seed, and in the subtropics the secret is early sowing into cooling autumn soil. It dislikes being transplanted, so sow where it is to grow, in full sun and free-draining ground. The seed germinates best when the soil is cool, which is why the April-to-June window is worth respecting rather than pushing.

The most common failure is poor or patchy germination, and warm soil is the usual cause. If you sow too early while the ground is still summer-warm, seed simply sits and rots. Waiting for the first proper cool spell, or refrigerating the seed for a week or two before sowing, sharply improves the strike. Sow a little more thickly than you think you need and thin the survivors.

Through the mild winter the plants grow slowly, then bolt upward in spring to flower. The humid tail of the wet season can bring fungal leaf spots and powdery mildew, so keep spacing generous for airflow and water at the base in the morning in a humid Lismore garden. Stake the tall spires against summer storms, and pick or deadhead spent flowers to prolong the display. One note for households: all parts of larkspur are toxic if eaten, so keep it clear of curious children and pets.

Larkspur at a glance

Common questions

When do I sow larkspur in Brisbane?

Sow direct from April to June, once the autumn soil has begun to cool. Larkspur needs that cool ground to germinate and will not strike reliably if sown into warm summer soil. An autumn sowing flowers the following spring.

Why won't my larkspur seeds germinate?

Warm soil is almost always the reason, since the seed needs cool ground to break dormancy. Wait for the first proper cool spell, or chill the seed in the fridge for a week or two before sowing. Sow a little thickly and barely cover it at 3 mm.

Can I transplant larkspur seedlings?

It is best not to. Larkspur resents root disturbance and often sulks or bolts after transplanting, so sow it direct where it is to grow and thin the seedlings instead. Direct sowing into cool autumn soil gives the strongest plants.

Is larkspur poisonous?

Yes, all parts of the plant are toxic if eaten, so site it away from young children and pets. It is grown purely as an ornamental for its tall flower spires. Wash your hands after handling if you have sensitive skin.

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