When to plant Phlox in Tropical Australia
Tropical zone — applies to Darwin, Cairns, Townsville, Broome, Mackay and similar areas. Growing elsewhere? Temperate · Cool · Subtropical · Arid.
Sow annual phlox direct from March to September, scattering the fine seed just 3 mm deep where it is to flower. This dry-season window suits tropical gardens in Cairns, Townsville and Mackay, when lower humidity lets the seedlings establish without rotting. Germination takes 10–20 days, and plants flower quickly, in around 70 days. Space seedlings 10–15 cm apart in rows 20–30 cm apart for a dense, low mass of colour. Phlox dislikes transplanting, so sow direct and thin rather than moving seedlings once they are up.
Sowing calendar — tropical zone
Green months are your sowing window: March to September.
Growing notes
Annual phlox is a fast, cheerful dry-season filler in the tropics, giving colour in around 70 days from a direct sowing. It wants full sun and free-draining soil, and rewards a modest sowing with a solid low carpet of bloom. Because it flowers so quickly, you can fit successive sowings across the dry season for continuous colour.
The main failure mode is humidity-driven fungal disease. In warm, damp air phlox is prone to powdery mildew and stem rot, especially if plants are crowded or watered over the leaves. Keep to the March to September window, water at the base, and thin seedlings to the recommended 10–15 cm so air moves between plants. If mildew appears, remove affected growth and improve spacing next time.
A couple of practical notes:
- Sow direct and thin, since phlox resents root disturbance and sulks after transplanting.
- Deadhead lightly to stretch the flowering period.
- Do not overfeed, as lush soft growth is more prone to disease in the tropics.
Sow the last batch by September so plants finish flowering before the November wet season brings the humidity that ends their run.
Phlox at a glance
| Sowing depth | 3 mm |
|---|---|
| Plant spacing | 10-15 cm |
| Row spacing | 20-30 cm |
| Germination | 10-20 days |
| Days to maturity | 70 days |
| Frost tolerance | Hardy |
| Method | Raise Seedlings,Sow Direct |
Common questions
- When do you plant phlox in the tropics?
- Sow direct from March to September, across the drier part of the year. Lower dry-season humidity lets phlox establish and flower without the fungal problems that plague it in wet conditions. It flowers fast, in about 70 days, so successive sowings work well.
- Why does my phlox get powdery mildew?
- Warm, humid air and crowded plants encourage powdery mildew on phlox. Thin seedlings to 10 to 15 cm for airflow, water at the base rather than over the leaves, and remove affected growth. Sticking to the dry-season window reduces the risk.
- Can you transplant phlox seedlings?
- It is better not to. Phlox resents root disturbance and often sulks after transplanting, so sow the seed direct where it is to flower and thin the seedlings to spacing instead. Sow just 3 mm deep, as the seed is fine.
- How long does phlox take to flower?
- Annual phlox is quick, flowering in around 70 days from sowing. This makes it a useful fast filler for dry-season colour and means you can sow several batches in succession before the wet season arrives.
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