How to Grow Aster
'Giants of California' from Seed
Bred for the professional cut flower trade in Santa Maria, California — massive double pom-pom heads in a sophisticated palette of rose, violet, peach and crimson on exceptionally long 60–70cm stems, lasting up to two weeks in the vase
'Giants of California' is not a hyperbolic name. The flowers genuinely are enormous — fully double, densely petalled pom-pom heads that can reach 8–10cm across, carried on stems of 60–70cm that are among the longest produced by any China aster variety. This strain was developed specifically for the commercial cut flower trade in Santa Maria, California — a region with near-perfect growing conditions for asters — and the breeding priorities of that trade are evident in every quality the plant delivers: stem length, flowerhead size, vase life, and a colour palette of sophisticated grown-up tones that works beautifully in professional arrangements.
The Fleuroselect Quality Mark that 'Giants of California' carries is awarded to varieties demonstrating outstanding garden performance and unique flower form — recognition that this is not simply a larger version of a standard aster but a genuinely different and superior growing experience. The yellow centre of a conventional aster is buried so deeply under the layers of petals that it is invisible until the flower is very old, giving the flowerhead a luxurious, opaque, velvet quality quite unlike any other China aster type. In the vase, conditions permitting, the flowers can last up to two weeks — exceptional longevity for a summer annual.
Quick Facts at a Glance
Plant Type
Half-Hardy Annual
Sowing Time
Mar–Apr indoors
Flowering Months
August – October
Position
Full sun; well-drained
Height & Spread
60–70cm · 30cm
Difficulty Rating
4 out of 5 — Requires care
Understanding the Plant
'Giants of California' belongs to the ostrich-plume type of Callistephus chinensis — a classification referring to the loose, layered, slightly reflexed petal arrangement that gives the flowerheads their full, fluffy appearance rather than the tightly incurved form of varieties like Duchess Mixed or Peony Mix. The petals are numerous and densely packed but they carry a slight softness and movement rather than the rigid incurved precision of chrysanthemum-type asters, which gives the overall head a more naturalistic, garden-gathered quality.
Like all China asters, 'Giants of California' is susceptible to aster wilt — a soil-borne fungal disease caused by Fusarium oxysporum — and crop rotation is the non-negotiable management strategy. Never plant in the same soil two seasons running. The investment in selecting a new bed position or using fresh container compost each season is repaid in the health and vigour of the crop.
The California Cut Flower Heritage
The Santa Maria Valley in California became one of the world's most important commercial cut flower production regions in the twentieth century, with its mild climate and intensive agriculture producing flowers for markets across North America. The 'Giants of California' strain was developed here specifically to meet the demands of professional florists: maximum stem length, maximum flowerhead size, and maximum vase life. Growing it in a UK garden is growing a piece of that professional heritage — a variety designed to perform at the highest level, which it does reliably when given the soil management and care it requires.
⚠️ Aster Wilt — Rotate Every Season
Fusarium wilt can devastate a China aster planting with sudden, irreversible collapse. There is no cure — only prevention through crop rotation. Never plant China asters in the same soil two consecutive seasons. The fungus persists for three to five years in infected soil. Growing in containers with fresh compost each year eliminates the risk entirely. This applies equally to all China aster varieties.
When & How to Sow
'Giants of California' flowers later than most other asters — its main display runs from August to October, with peak flowering in August and September. Sow indoors in March or April for this window; a February sowing risks the seedlings becoming rootbound before it is safe to plant out.
Rotation First — Then Sow
Before sowing a single seed, decide where this year's asters will be planted. Confirm that no China asters have grown in that spot in the previous three to five years. If the garden is small and rotation is difficult, commit to container growing with fresh compost. This rotation decision is more important than any other aspect of growing China asters successfully.
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Sow indoors in March or April at 18–21°C. Sow onto moist seed compost and cover with a fine 3mm layer of vermiculite. Unlike surface-sown annuals, China asters benefit from this very fine covering, which helps retain moisture around the seed. Keep consistently moist at consistent warmth.
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Germination in 10–14 days. Move immediately to bright light once seedlings appear. Grow on at 12–15°C — cooler conditions produce sturdy, compact seedlings rather than drawn ones. Good airflow is essential; poor ventilation encourages damping off.
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Prick out into individual 7–9cm pots. Once seedlings have two true leaves. Grow on steadily, potting up once roots fill the container. Do not allow plants to become rootbound — stressed plants are more susceptible to disease.
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Harden off and plant out from late May to June. 30cm apart in their designated rotation bed or in containers. Water in well. Support tall stems in exposed positions with netting or stakes placed before stems reach 30cm.
Growing On Tips
Full Sun Essential
Full sun develops the richest colour and the strongest, most upright stems. 'Giants of California' produces its finest flowers with a minimum of six hours of direct sun daily. In shade, plants flower poorly and stems become weak, unable to support the heavy flowerheads without collapsing.
Support Those Heavy Heads
At 60–70cm with large, heavy flowerheads, 'Giants of California' needs support in any exposed position. Place horizontal netting at 30–40cm height early in the season, before stems reach that point. The stems grow up through the netting and are supported without being visibly constrained. In sheltered positions, well-grown plants are often self-supporting.
Crop Rotation
Move the aster bed to a new position every season without exception. Fusarium wilt persists in infected soil for three to five years and there is no cure. In small gardens where rotation is difficult, grow in large containers (minimum 30cm diameter) with fresh multipurpose compost each season — this eliminates wilt risk entirely.
Consistent Moisture
China asters are shallow-rooted and wilt under drought stress — which also reduces their disease resistance. Keep soil consistently moist throughout the season. Water at the base only; overhead watering creates conditions favourable to fungal problems. Mulch around plants to retain moisture and reduce watering frequency.
Feeding for Size
To develop the maximum flowerhead size that makes 'Giants of California' exceptional, feed fortnightly with a balanced liquid feed from planting out. Switch to a high-potash feed from late July. Well-fed plants produce significantly larger heads than unfed ones — nutrition is one of the key variables in realising the variety's full potential.
Cutting at Peak
Cut when flowerheads are three-quarters open to fully open — the large heads of this variety continue to develop fully in water if cut at the three-quarter stage. Remove all foliage below the water line. Condition in deep cool water for several hours before arranging. Vase life is 10–14 days in a cool room — exceptional for an annual.
Common Problems & How to Fix Them
| Problem | Likely Cause | What to Do |
|---|---|---|
| Fusarium wilt — sudden collapse | Soil-borne fungal disease | No cure exists. Remove and destroy affected plants immediately without composting. Do not plant China asters in the same ground for three to five years. Use fresh compost in containers next season. Rotation is the only effective prevention. |
| Stems toppling | Insufficient support; heavy heads | Install horizontal netting support at 30–40cm before stems reach this height. The large flowerheads of this variety are particularly susceptible to wind damage. In exposed positions, support is non-negotiable. |
| Aphids on stems and growing tips | Common late spring to summer pest | Inspect regularly from May onwards. Knock off with a jet of water or apply insecticidal soap. Aphids can transmit aster yellows disease so prompt control matters. Encouraging natural predators with companion plantings of alyssum or phacelia helps maintain populations. |
| Damping off in seedlings | Overwatering, cold, poor ventilation | Water from below only. Ensure good airflow from germination. Maintain warmth consistently. Thin seedlings promptly if overcrowded. Remove any collapsed seedlings immediately to prevent spread. |
| Flowers smaller than expected | Underfeeding, drought stress, or poor rotation | Feed fortnightly from planting out. Maintain consistent moisture. Ensure the site has not grown asters previously. Well-grown plants in fresh, fertile ground with adequate moisture and feeding produce the full giant flowerheads this variety is capable of. |
When to Expect Flowers
'Giants of California' is a later-flowering variety than Duchess Mixed — its main display runs from August through to October, with the peak cutting period in August and September. This later season is actually one of its greatest assets, as it arrives when many summer annuals are declining and the cutting garden is in most need of something spectacular. In mild autumns, the flowers continue right to the first hard frosts of October.
Sow indoors in March or April — the enormous double heads appear from August and continue to October, providing the late-season cutting garden's most spectacular display on stems up to 70cm long.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
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| 🌱 Sow Indoors |
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| 🪴 Plant Out |
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| 🌸 Flowering |
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Plant Specifications
The aster that the professional cut flower trade built its reputation on
'Giants of California' is the aster for gardeners who want the biggest, most professional-quality stems from their late summer cutting patch — the variety that florists reach for, that wedding arrangers specify, and that stops conversations when a vase of it sits on the table. Rotate the bed, support the stems, feed consistently, and this Fleuroselect-winning variety will produce stems of 60–70cm carrying flowerheads so large and so densely petalled they seem almost too extravagant to be real. The cutting garden's grand finale deserves something this spectacular.
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