The short-lived annual dianthus lack nothing of the charm of the perennials, except scent.
The idea of a garden without dianthus of some kind is as sad as one without a rose or daffodil. They are a varied bunch and include alpine pinks and florist’s carnations as well as sweet Williams. Most are perfect for picking and most are very fragrant, but not all. They are generally sub-shrubby with a woody base and narrow, often glaucous leaves. Most of the perennials flower in early summer. The typical garden pinks bloom in June but the Allwood hybrid pinks bloom all summer, after an initial early summer flush. Most are hardy but hate poor drainage. Most are tolerant of, or prefer, alkaline soils. None are very long lived and garden pinks are at their best in their second year, declining after their third. They are easily increased by cuttings. Sweet Williams are biennial and are usually sown in early summer, to bloom the next year but they can also be propagated by cuttings if a plant is exceptional.
The annuals pinks are rather ignored, though modern hybrids, usually (I think) involving the sweet William (Dianthus barbatus) with Dianthus chinensis, are commonly sold as pot plants in bloom, both in spring and summer. Dianthus chinensis is strictly perennial but is grown as an annual, flowering freely the first year when treated as a half hardy annual. It has bright, often zoned flowers but little scent.
The old strain ‘Baby Doll’ was among the first plants I ever grew from seed, when I was about 9, so you can tell how ancient it is! Plants are very compact, about 15cm tall, and the flowers are huge (above) in a wonderful mix of colours. The flowers have the faintest scent. Although treated as an annual, plants will survive an average winter (whatever that is) and flower the next year but I find that they exhaust themselves after the second flush of bloom and die in early summer.
I am not sure of the difference between D. chinensis and var. heddewigii, but the latter has several seed strains assigned to it including a ‘black’ and white double and mixtures of semi-doubles in a range of pretty shades. These tend to be taller than ‘Baby Doll’.
Sow seeds in mid March and transplant seedlings as with any half hardy annual. Mature plants can withstand frost but young seedlings should be protected from frost even though they can withstand cooler temperatures than many other bedding plants. Good light and avoiding too much water is essential. Plant out in a sunny spot for the most compact growth and best flowers.