When to Sow China Asters (Callistephus chinensis)
Share
Planning Your Aster Sowing Schedule for the Perfect Bloom
China asters — with their lush, romantic blooms and strong stems — are among the most rewarding annuals to grow for late-summer and early-autumn bouquets. Timing, however, is everything. Getting your sowing dates right will determine how abundant and high-quality your flowers will be.
Understand Your Frost-Free Date
Before you sow, the most important thing to know is your last spring frost date (also called the frost-free date).
This date can change slightly each year depending on the weather.
For example, in 2026 the estimated frost-free date is May 5th, 2026 (05/05/2026).
All other sowing and transplanting times are counted backward or forward from this date.
General Timing Guide
|
Step |
Timing |
Description |
|---|
|
Indoor Sowing |
6 weeks (≈ 42 days) before the last frost |
Start your seeds indoors to give them a strong, healthy start. Maintain 21–22 °C and keep the soil evenly moist. |
|
Transplanting Outdoors |
After the frost-free date |
Move your plants to the garden once all danger of frost has passed and nights are mild. |
|
Successive Sowings |
Every 21 days |
For a longer flowering window, plan a second sowing three weeks after the first. |
|
Days to Maturity |
About 120 days from sowing |
That means asters sown in late April will begin flowering around August. |
Example Sowing Plan for 2026
|
Sowing Round |
Sowing Date |
Transplanting |
Expected Bloom |
Type |
|---|
|
1st Sowing |
April 23, 2026 |
Mid–May |
Early August – Mid-September |
MP – Main Producer |
|
2nd Sowing |
May 14, 2026 |
Late May |
Late September – October |
MP – Main Producer |
For China asters, two sowings per season are enough to ensure a continuous, beautiful flowering period right through autumn.
Grower’s Notes
- Start seeds indoors in trays or small pots 6 weeks before your frost-free date.
- Transplant only once the soil has warmed and all frost danger is past.
- Maintain consistent watering and support stems with a horizontal net as they grow.
- Succession sowing helps stagger bloom times and ensures fresh stems for harvesting.
In Short
- Last frost example (2026): May 5 (05/05/2026)
- Days to maturity: 120
- Sow indoors: 42 days before last frost
- Successive sowing gap: 21 days
- Recommended sowings: 2 per season (Main Producer crop)
Therapy of Flowers Tip
For the most beautiful, long-stemmed asters, keep them stress-free during early growth — steady light, warmth, and moisture make all the difference. With just two well-timed sowings, you’ll have armfuls of pastel blooms from August until frost.
Sowing & Cultivation
Transplanting is recommended for best results.
- Sow indoors: 6–8 weeks before the last frost.
- Sowing depth: 0.3 cm (⅛ inch).
- Germination temperature: 21–22 °C.
- Germination time: 10–14 days.
- After germination: Maintain 21 °C by day and 16–17 °C by night.
Transplant seedlings into cell trays or 7–10 cm pots once the first true leaves appear. Avoid root binding. Harden off plants before transplanting outdoors.
Transplant outdoors: After frost danger has passed, spacing plants 15–30 cm apart. Black or IRT mulch helps warm the soil and suppress weeds.
For direct sowing, plant 0.3 cm deep in 18–21 °C soil after frost. Thin to the same spacing.
