GardenersHQ

How to Grow Dianthus barbatus Plants in your Garden

Gardener's HQ Guide to Growing Sweet William

Dianthus barbatus is a biennial member of the Dianthus genus and usually goes by the name of Sweet William. Despite being a biennial or even a short-lived perennial it is usually grown as an annual in the garden. This is achieved by using cold treated plants from gardening centres and nurseries. As the plant readily self-seeds once it is in place more Sweet William plants will bloom each year. However these may not stay true to the original cultivar, so you may wish to remove these and grow purchased plants yearly.

The main Dianthus genus can come in many forms; annuals and perennials include the carnations, whereas the biennials include Sweet William. This page is dedicated to the biennial Dianthus barbatus, Go here for information on How to Grow Carnations and Pinks

Dianthus barbatus
Dianthus barbatus Harlequin Cultivar photograph by 阿橋 HQ; CC.

Sweet Williams and other Dianthus plants tend to have a bushy nature and grow from 30 to 75 cm in height.

Sweet William leaves


Dianthus

Flowers may be red, violet white or pink when one coloured; however Dianthus can often have double and triple coloured flowers, that are singular or double petalled; often with serrated edges.

Quick Growing and Care Guide

  • Scientific Name: Dianthus barbatus
  • Common Name (s): Sweet William, Bearded Pink
  • Growing Zone (USA / UK Hardiness): 3 to 9 / H7

Plant Details

  • Life Cycle / Plant Type: Biennial. Cold treated plants are grown as an annual in the garden.
  • Plant Height: One to two feet (30 to 60 cm)
  • Plant Spread: 6 to 12 inches (15 to 30 cm)
  • Blooms: Late Spring through summer.
  • Flower Details: Fragrant. Dainty. Umbel of up to 30 flowers. five petals. Serrated. Wild-type flowers are red with base of white. Cultivars include many colours such as pink, white, purples and bi-coloured. Double-flowered cultivars also available.
  • Leaf Foliages: Tapered. Lance-shaped. Blue-green. 1 1.2 to 4 inches long (4 to 10 cm).

Growing Conditions

  • Best Light Conditions: Full sunlight through to partial shade.
  • Suitable Soil Types: Well drained. Deep. Organic.
  • Suitable Soil pH: 6.0 -to 7.5
  • Soil Soil Moisture: Moist
  • Sowing, planting, and Propagation:
    Seeds do not stay true. Naturally reseeds. Sow seeds towards the end of spring and transplant to final location in autumn.
    Propagate cuttings in late spring or early summer from slips (side growth shoots). Remove leaves from the bottom inch (2.5 cm) of the slip. Dip in rooting powder. Cuttings should then be poked into seed starting potting soil in trays. Grow in the shade. Mist to keep moist. Cuttings can also be took from the root. Transplant in late spring. Cold treated plants can be planted in the autumn and will bloom the next year.
  • Care: Deadhead flowers. Water to keep soil moist. Do not get water on plant. Apply Feed to the soil surrounding the Sweet William plant (water-soluble fertilizer: once per month, or per fortnight in poorer soils).

Further Information

  • Best used for: Ornamental plant, Border, Massed planting.
  • Family:
  • Closely Related Species:
  • Miscellaneous: Deer Tolerant. Attracts wildlife such as birds and butterflies to the garden.
  • Family: Caryophyllaceae (pinks), Closely related species and genera: Agrostemma; Baby Breath Flowers; Silene plant
  • Further Reading and References used for this Biennial Dianthus genus growing guide: RHS; Wikipedia

How to Grow Sweet William (Dianthus)

If sowing sweet William seeds outdoors then they should be sown at a depth of about 7 mm into a sunny part of the garden (from mid spring to July). They should be grown with a spacing of 20 to 25 cm apart in a deep and rich slightly acidic to neutral soil (pH 6 to 7). Sweet William is a biennial so will flower in the second year. if you prefer to start seedlings of Sweet Williams off indoors then they should be started about 8 weeks before they are transplanted into the garden in autumn (or late spring). Germination at a temperature of about 20 degrees Centigrade takes from one to two weeks.

Caring for Dianthus

If you require more Dianthus plants then cuttings can be took from the root.