Callistephus chinensis Seeds | China Aster
LATIN NAME: Callistephus chinensis
COMMON NAME: China Aster
Plant Profile
Callistephus is monotypic, which is unusual among the temperate members of the daisy family and worth remembering when reading older literature: the many names and varieties there all refer to forms of Callistephus chinensis. The plant is an annual, an upright herb with toothed, alternate leaves and flower heads carried on stiff stems, and the genus sits in the tribe Astereae alongside the asters it is so often confused with.
The wild form has a single row of purple ray florets around a yellow disc. The ray florets in modern cultivars have been multiplied, lengthened and sometimes quilled, but the underlying structure is unchanged: a receptacle bearing female ray florets at the margin and bisexual disc florets at the centre, all enclosed in overlapping bracts before opening.
The most serious disease of China aster is aster yellows, caused by a phytoplasma, a wall-less bacterium that lives in the phloem. It is carried from plant to plant by the aster leafhopper, which injects the organism as it feeds. The symptoms are unmistakable once the flower opens: the parts that should be coloured stay green, the head proliferates into a tuft of leafy shoots, and the plant is sterile. There is no cure, so management means controlling the vector and removing affected plants.
Walk the rows as the buds colour and pull out anything greening, thickening or throwing abnormally leafy shoots, roots and all, because a plant left in place is a reservoir for the leafhoppers working through the bed. Keeping flowering weeds down along the edges removes the other hosts that keep the vector’s population topped up.
Science & Biotechnology
The colour palette rests on two pigment families. The pinks, reds, purples and blues come from anthocyanins, mostly cyanidin and delphinidin glycosides, and the exact shade depends on how those molecules are decorated with sugars and acids and on the acidity of the cell sap. The yellows and cream tints come from carotenoids and flavone copigments, which also stabilise the anthocyanins.
Uses & Benefits
The doubled forms arise when stamens and sometimes the disc florets develop as petal-like structures instead of reproductive organs, a homeotic shift in floral organ identity that breeders have exploited in many ornamentals. Selecting for that conversion, and then for longer and more numerous ray florets, produced the cactus flowered, ostrich plumed and pompon classes, and it is why the most doubled forms set little seed.
Because the best cutting types are maintained vegetatively, they accumulate viruses, which is why meristem-tip culture is used to produce clean stock: the tip of a growing shoot is excised and grown on in vitro, well ahead of most virus particles, and the plantlets are bulked up in isolation. It is the same principle used for potatoes and strawberries, and the reason named aster lines stay true in the trade.
Growing from Seed
The second disease to plan around is Fusarium wilt of aster, a soil-borne fungus that enters through the roots, blocks the water-conducting tissue and leaves plants wilting while the stems stay green. It persists in the soil for years, so a bed that has carried a sick crop should not grow asters again for a long time; rotate with unrelated plants, and choose cultivars that carry resistance.
As a cut flower the China aster is hard to beat at the end of the season: the stems are straight, the heads are substantial and they last well in water if the lower leaves are stripped and the water changed. In the border the smaller forms make dense bedding and the tall ones give height to a late planting. The flowers are also worked by bees and hoverflies, worth remembering when choosing between a heavily doubled show form and an open one.
Sow thinly in a tray of moist seed compost, cover the seed only lightly, and keep the tray warm until the seedlings appear. Prick them out into individual pots once they have two true leaves, and move them to a cool, bright place, because warmth and crowding produce the soft, leggy growth that snaps in the wind. Plant out once they stand about ten to fifteen centimetres tall, at about thirty centimetres apart.
Our Take
I sow these for the vase rather than the border, and I never plant them in ground that has had asters in it before, which has saved more crops than any spray. New England aster gives a perennial version of the same late colour and the same leafhopper problem, so I keep the two apart. Chrysanthemum is the other great autumn cut flower and takes the same pinching, and calendula is the easy annual that fills the rest of the cutting bed while the asters come on. Rotate the ground, rogue the green flowers, and cut them just as the outer florets open.
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