Sweet william (Dianthus barbatus) is a short-lived hardy perennial, loved for its showy display of colourful summer flowers. The foliage forms low rosettes of non-spreading mid-green or bronze-green leaves. Large flower clusters are borne on sturdy stems up to 60cm high, made up of many individual florets with a surrounding ‘ruff’ of green foliage. Flower colours come in shades of pink, purple, red, dark maroon, and white, and blooms are often bicoloured, too. Sweet william is hardy, easy to grow from seed, and makes an excellent cut flower.
Traditionally sweet william has been grown as a biennial, sown in spring to bloom in early summer the following year. However, the introduction of quick-flowering varieties means these can be treated as annuals to bloom in the same year from an early spring sowing. If deadheaded promptly, sweet william may come back the following year but is unlikely to live beyond two years – it’s best to view any flowering after the second year as a bonus.
How to grow sweet william
Sow seed of sweet william in early spring or early summer, depending on whether the variety is to be treated as an annual or biennial. Grow in small pots until well established, then transplant into flowering positions. Alternatively, buy young ‘plug’ plants to pot up and grow on, in late summer, or buy sturdy ready-grown plants in early autumn. Once flowering has finished, cut stems to the ground.
Where to grow sweet william
Grow in full sun to achieve the best flowers, on soil that is well drained, ideally with a neutral to slightly acid pH, though sweet williams tolerate a wide range of growing conditions. Grow in borders, bedding displays, and as a gap-filler. Shorter-growing varieties are good in containers, though sweet william isn’t suited to hanging baskets due to its upright habit.
How to plant sweet william
Sow seed in early spring or early summer and prick out into small pots or modular trays. Plant out in summer or early autumn. To grow as a cut flower, sow in the ground in rows and thin the resulting seedlings to at 30 cm apart. Alternatively, buy ready grown plants at planting time.
How to care for sweet william
Once planted, keep watered until established. Sweet williams in containers need regular watering. Once flowers have finished, cut the whole stem back to the ground to improve the plants’ chances of continuing to grow for another season.
Pests and diseases
Sweet william is generally free of pests and diseases, given the right growing conditions.
Advice on buying sweet william
- Sweet william is widely available as seed, as plug plants to pot up and grow on, or as garden-ready plants, both online and from nurseries and garden centres
- Growing your own from seed gives the widest choice of varieties and the opportunity to choose individual colours, as plants and plugs of sweet william are usually a mixture of colours
- Always check plants for signs of pests and diseases before planting
Where to buy sweet william
Types of sweet william to grow
Sweet william ‘Barbarini’ – dwarf variety, perfect for pots. Height x Spread: 20cm x 20cm
Sweet william ‘Purple Crown’ – bears large clusters of purple and white flowers H x S: 60cm x 30cm
Sweet william ‘Rockin Red’ – interspecific hybrid bearing bright red flowers with a spicy fragrance. H x S: 50cm x 30cm
Sweet william ‘Indian Carpet’ – a dwarf variety mix, bearing flowers in red, rose and white. H x S: 15cm x 15cm
