How to Grow Aster
'Duchess Mixed' from Seed
The late summer workhorse of the cutting garden — large incurved chrysanthemum-like heads in rich mixed colours from July to October, when most other annuals are fading, and outstanding as a long-lasting cut flower
The China aster — Callistephus chinensis — occupies a particular and valuable position in the cutting garden calendar: it is one of the finest and most productive annuals for late summer and autumn colour, flowering vigorously from July through to October when many other summer annuals are declining and the gap between summer and autumn flowers is felt most keenly. 'Duchess Mixed' is one of the most reliable and most spectacular forms — an upright, strong-growing variety producing large, incurved, chrysanthemum-like flowerheads in a rich range of colours including deep crimson, pink, lavender, purple, white, and all the gradations between.
China asters are not the easiest of annuals — they are susceptible to a soil-borne fungal disease called aster wilt that can devastate a planting, and they benefit from specific soil management practices. But for gardeners who grow them well, they provide some of the most impressive and most long-lasting cut flowers available from a summer sowing, with individual stems lasting a week or more in the vase and plants that produce cutting material continuously from July until the first hard autumn frosts arrive.
Quick Facts at a Glance
Plant Type
Half-Hardy Annual
Sowing Time
Feb–Apr indoors only
Flowering Months
July – October
Position
Full sun; well-drained
Height & Spread
60cm · 30cm, bushy
Difficulty Rating
4 out of 5 — Requires care
Understanding the Plant
Callistephus chinensis — the China aster — is a single-species genus originating from China and Korea, now grown worldwide as an ornamental annual. Despite the common name, it is not closely related to the perennial asters (now largely reclassified as Symphyotrichum). It belongs to the same daisy family (Asteraceae), and the Chinese name June菊 reflects its long history in Chinese cultivation. The species has been grown in European gardens since the early eighteenth century.
'Duchess Mixed' is a tall, incurved variety — the petals of each flowerhead curve inward toward the centre, creating the rounded, chrysanthemum-like form that distinguishes this type from flat-petalled or quilled varieties. The individual flowerheads reach 6–8cm across, carried on strong upright stems at 60cm. The mix includes the full classic colour range of China asters — crimson, deep pink, lilac, purple, lavender, white and soft rose — providing considerable variety from a single packet.
⚠️ Aster Wilt — The Main Challenge
Aster wilt is a soil-borne fungal disease caused by Fusarium oxysporum f. sp. callistephi, which can devastate China aster plantings without warning. Affected plants wilt suddenly and collapse, often shortly after beginning to bud. There is no chemical cure — prevention is the only management strategy. The most important preventive measure is crop rotation: never plant China asters in the same soil two years running, as the fungus persists in infected soil for many years. In practice, this means moving the aster bed to a new location each season, or growing them in containers with fresh compost. Good drainage and avoiding overwatering also significantly reduce risk.
The Late Season Value
'Duchess Mixed' flowers from July through October — the period when many summer annuals are declining and the cutting garden needs reinvigorating. It bridges the gap between the main summer flush and the arrival of autumn flowers, and in October it often provides the most vibrant colour in the whole garden at a time when most other annuals have succumbed to the first frosts. Growing it in a cool greenhouse or conservatory extends the season further into November in exceptional cases.
When & How to Sow
China asters must be started indoors — direct sowing outdoors is not recommended as germination requires consistent warmth that UK outdoor conditions cannot reliably provide in spring, and the plants need a long enough season to develop to cutting size before the summer flowering window arrives.
Rotation is Non-Negotiable
Before sowing, decide where this season's asters will be planted out — and confirm that China asters have not been grown in that soil in the previous three to five years. Aster wilt persists in soil for years. If the only available positions have had asters recently, grow in containers with fresh compost. This rotation decision is more important than any other single growing technique for China asters.
-
Sow indoors from February to April at 15–20°C. Sow into trays or modules of seed compost. Unlike most annuals in this guide, China asters can be lightly covered — push seed to approximately 0.5cm depth or cover with a very thin layer of sieved compost. Some sources recommend surface sowing with light access; either approach works.
-
Germination in 14–21 days. Keep consistently moist at 15–20°C. Move to good light as soon as seedlings emerge — asters grow quickly and draw in low light. Ventilate well once seedlings are established; poor airflow encourages damping off.
-
Prick out when large enough to handle. Into individual 7cm pots or cell trays. Grow on in cool but frost-free conditions — asters prefer cooler growing temperatures than many half-hardy annuals. Over-warm growing conditions produce drawn, weak plants.
-
Harden off carefully over two weeks. Begin outdoor acclimatisation from late April but protect from frost. Plant out from late May to June, 30cm apart, in their designated rotation bed. Water in well and keep consistently moist in the early weeks of establishment.
Container Growing — The Wilt-Safe Option
Growing China asters in large containers (minimum 30cm diameter) filled with fresh, peat-free multipurpose compost each season is the most reliable way to avoid aster wilt entirely. The fresh compost contains no Fusarium spores, and the containers can be reused with new compost each year without any disease risk. Feed weekly with a balanced liquid fertiliser from June and water consistently — containerised asters in sunny positions can be exceptional performers.
Growing On Tips
Full Sun
Full sun is required for the strongest, most upright growth and the richest flower colour. In shade, asters become leggy and flower poorly. A minimum of six hours of direct sun per day produces the best results. South or west-facing positions are ideal.
Crop Rotation
Never plant China asters in the same soil in consecutive years. Aster wilt fungi (Fusarium) persist in soil for three to five years — rotating to a new bed position each season is the most effective preventive measure available. Mark the aster bed position on a garden plan to avoid inadvertent repeat planting.
Watering
Keep soil consistently moist throughout the season — asters wilt under drought stress and this stress also makes them more susceptible to disease. Water at the base of the plant, not overhead — wet foliage creates conditions favourable to fungal problems. Mulch to retain moisture and reduce the frequency of watering needed.
Feeding
Apply a balanced liquid fertiliser fortnightly from planting out. Switch to a high-potash feed from late July to sustain flower production through August and September. Well-fed plants produce significantly more and larger flowerheads than unfed ones, and feeding also improves the plant's resilience against environmental stress.
Cutting Technique
Cut when flowerheads are approximately three-quarters open — fully opening in the vase gives the maximum display period. Cut early in the morning with long stems. Remove all foliage below the water line. Condition in deep cool water for several hours before arranging. Vase life is typically seven to ten days.
Greenhouse Extension
Plants in containers can be moved into an unheated greenhouse or conservatory before the first autumn frosts, extending the cutting season by two to four weeks into November. This is one of the most effective ways to maximise the value of China asters, which are at their best in September and October precisely when outdoor conditions are becoming inhospitable.
Common Problems & How to Fix Them
| Problem | Likely Cause | What to Do |
|---|---|---|
| Aster wilt — sudden collapse | Fusarium oxysporum soil-borne fungal disease | There is no cure for infected plants — remove and destroy immediately without composting. Do not plant China asters in the same soil for at least three to five years. Next season, use fresh compost in containers or a completely new bed position. Crop rotation is the only effective management strategy. |
| No germination | Too cold, too dark, or poor seed | Maintain 15–20°C consistently. Sow at 0.5cm depth or surface-sow with good light. China asters germinate in 14–21 days in good conditions. Ensure the compost is moist but not waterlogged throughout. |
| Leggy, weak seedlings | Insufficient light or too warm | Move to maximum light immediately after germination. Grow on in cool conditions — asters prefer 12–15°C after germination. Drawn seedlings can be potted on slightly deeper to provide additional stem support. |
| Aphids on growing tips | Common on aster seedlings and young plants | Check growing tips regularly from May onwards. Knock off with a jet of water, apply insecticidal soap, or encourage natural predators by growing companion alyssum nearby. Aphids on asters can transmit virus diseases — control promptly. |
| Flowers small or few | Underfeeding, poor drainage, or compact spacing | Feed fortnightly. Ensure 30cm spacing to allow for the bushy spread of each plant. Check drainage — asters in waterlogged soil produce significantly reduced flowering. Ensure full sun. |
| Plants dying in mid-season | Either aster wilt or root issues from poor drainage | Aster wilt produces sudden collapse without yellowing. Poor drainage causes gradual decline with yellowing lower leaves. Either way, remove affected plants, improve drainage for next season, and rotate to a new position. Do not replant in the same spot. |
When to Expect Flowers
From a February or March sowing, 'Duchess Mixed' typically begins flowering in July — occasionally late June in a warm season from an early February sowing. The main display period runs from July through September, with October flowering in mild years or when plants are under cover. The peak cutting period is August and September, when the flowers are at their largest and the colour is most vivid. A container-grown planting brought under cover in late September continues providing stems through October and into November.
Sow indoors from February and plant out in late May — the large incurved flowerheads appear from July and continue until the first hard frosts, providing the late summer cutting garden's most substantial and most colourful display.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 🌱 Sow Indoors |
|
|
|
|||||||||
| 🪴 Plant Out |
|
|
||||||||||
| 🌸 Flowering |
|
|
|
|
Plant Specifications
The late summer cutting garden's most spectacular performer
China asters ask a little more of the gardener than most annuals — crop rotation, consistent moisture, attentive feeding — but they repay the care with some of the most impressive and most long-lasting cut flowers you can grow from seed in a UK garden. In August and September, when many other annuals are declining, a well-grown planting of 'Duchess Mixed' is at the absolute height of its performance: large, incurved chrysanthemum-like heads in rich mixed colours on strong, upright stems, cutting beautifully for seven to ten days in the vase. Grow them, rotate them, feed them — and let them carry the cutting garden through autumn in considerable style.
Shop Aster Duchess Mixed Seeds →