Sweet William (Dianthus barbatus)

Sweet John, Sweet William

If you are looking to add a dash of colour and beauty to your garden, Dianthus Barbatus is an exceptional choice for you. Despite being a biennial or a short-lived perennial, it is typically grown as an annual by gardeners. Widely known for its ornamental value, it can be used as a gorgeous border plant or to beautify your patio as a container plant. Read on to learn more about growing and maintaining Dianthus Barbatus in your garden.

I. Appearance and Characteristics 

Dianthus barbatus, the sweet William, is a species of flowering plant in the family Caryophyllaceae, native to southern Europe and parts of Asia. It has become a popular ornamental garden plant. 

The exact origin of its English common name is unknown but first appears in 1596 in botanist John Gerard’s garden catalogue. The flowers are edible and may have medicinal properties. Sweet William attracts bees, birds, and butterflies.

Sweet William grows in the mountains of southern Europe from the Pyrenees east to the Carpathians and the Balkans, with a variety disjunct in northeastern China, Korea, and southeasternmost Russia. It grows to 13–92 cm tall (depending on the variety), with green to glaucous blue-green tapered leaves 4–10 cm long and 1–2 cm broad. The flowers are produced in a dense cluster of up to 30 at the top of the stems (known as an umbel) and have a spicy, clove-like scent; each flower is 2–3 cm diameter with five petals with serrated edges; in wild plants the petals are red with a white base.

There are two varieties:

  • Dianthus barbatus var. barbatus. Southern Europe. Leaves broader, up to 2 cm broad.
  • Dianthus barbatus var. asiaticus Nakai. Northeastern Asia. Leaves slender, not over 1 cm broad.

Planting sweet William in late spring will usually produce flowers the following year, although some new cultivars bloom in the first year if you start the seeds early enough. Research suggests that sweet William is mildly toxic to pets and people.

English name

Many legends purport to explain how sweet William acquired its English common name, but none is verified. It is often said to honor the 18th century Prince William, Duke of Cumberland. As a result of the Duke’s victory at the Battle of Culloden and his generally brutal treatment of the king’s enemies, it is also claimed that the Scots sometimes call the flower “stinking Billy”. 

Though this makes a nice story, it is entirely untrue. The Scots sometimes refer to the noxious ragwort as stinking willy in memory of the infamous Duke. Phillips speculated that the flower was named after Gerard’s contemporary, William Shakespeare. It is also said to be named after Saint William of York or after William the Conqueror. Another etymological derivation is that william is a corruption of the French oeillet, meaning both “carnation” and “little eye”. Sweet William is a favorite name for lovelorn young men in English folkloric ballads, e.g., “Fair Margaret and Sweet William”.

II. How to Grow and Care

Easy to grow when provided with filtered sun and rich, well-drained soil, these plants self-seed each year when given optimal growing conditions, so you might have a fresh batch of beautiful flowers to admire every summer. Space sweet William plants about 8 inches apart as bedding plants to allow for the dense foliage that appears during the first year. Sweet William plants are slow spreaders so there’s no need to worry about this plant overstepping its boundaries.

Sunlight

As important as it is not to have poor drainage in your rock gardens, this herbaceous perennial loves full sun compared to shade. The Dianthus plant can thrive in light shade but become leggy and flop. While in warmer regions, some partial shade helps in the afternoon to help encourage additional blooming.

Temperature and Humidity

For a flowering plant, sweet William is relatively cold-hardy. It can survive light frosts, but deep freezes will result in the plant dying down. This species doesn’t do well with high humidity, and temperatures above 85° Fahrenheit can result in dormancy.

Watering

The Sweet William needs more water during the growing season, but please be careful not to overwater. As mentioned, when you plant Sweet William, spacing is vital as drainage, and when you overwater, it can lead to crown rot.

While Sweet Williams is drought tolerant to some extent, it still helps to check the soil moisture to see if your plants need water, and it also applies to container gardens. Still, if you find the rainfall is less, you may need to water more often when your plant is in full sun.

Soil

Sweet William can tolerate many soil types, except wet, heavy conditions. A well-drained, fertile, loamy site is ideal. The plants can survive in soils with various pH levels too but often do best in a neutral to slightly alkaline one. Some growers add lime to the soil before planting.

Fertilizing

Sweet william should be fertilized every month-and-a-half to two months with a slow-release balanced fertilizer with an N-P-K ratio of 5-10-5. Note that this fertilization regime only applies to the spring and summer growing season, and the plant doesn’t need to be fertilized at other times.

Planting Instructions

Plant your Sweet William Dianthus up to 12 inches apart to provide adequate air circulation, but it can vary from one species to another. It helps to loosen the soil to a 12-inch depth and fill it with compost. Also, dig a hole twice the size of the root ball to place inside the hole.

Another helpful tip is to keep the top of the root ball level with the soil and tamp the soil around the base and water. The good news is that they are slow spreaders when you grow Sweet William and will not overstep its boundaries fast.

Pruning

When it comes to your Sweet William in mass plantings, you can protect them from the winter cold by cutting back all the dead foliage and spent blooms.

But please do not do this in the fall; instead, let the dead leaves fall to the ground to provide a protective layer of mulch to insulate roots before removing the rest of the foliage.

If you grow Sweet William in containers, you can move them out of the wind, ice, and snow. Alternatively, you can deadhead flowers to encourage more blooming, as the perennial can bloom through to late summer.

Propagation

Propagating sweet William from cuttings is possible. However, because these plants are short-lived, many people simply purchase cold-treated plants during the spring to grow them as annuals.

Sweet William is easy to grow from seed, but they don’t typically bloom the first year. The seed can be sown into the ground in the late spring or early summer when there is no danger of frost. They prefer cool temperatures of around 50 to 55 degrees Fahrenheit and consistently moist soil for germination. Temperatures above 65 degrees Fahrenheit can result in weak, leggy growth.

These plants don’t like to be overcrowded, so, as the seeds germinate, thin them out so there is adequate air circulation.

If you want to see blooms in the first year of planting, you could try sowing the seeds indoors in cell packs or containers six to eight weeks before the last spring frost. Harden them off and transplant the seedlings outside once the danger of frost has passed.

Overwintering

Protect your sweet William plants from the winter cold by cutting back dead foliage and blooms after flowering, but don’t prune in the fall. Let the rest of the dead foliage fall to the ground to create a layer of protective mulch. Add to this a few more inches of mulch to insulate roots. If your plants are in containers outdoors, move pots away from areas that suffer from wind, snow, and ice.

Pests and Diseases

The most common pests are slugs found in the garden and snails. The other concern is overwatering, leading to crown rot, rust, and root rot. With insufficient air circulation and high humidity, powdery mildew can form on the foliage and invite spider mites.

III. How to Get Sweet Williams to Bloom

With their small clusters of flowers, sweet Williams offers a splash of color right through the summer. Under the correct conditions, sweet Williams can flower from May through to October in their flowering year. Their bright range of colors includes reds, pinks, whites, purples, and bicolors. Some flowers are fragrant, but many cultivars are scentless. Their fringed and bearded petals are what give them their alternative “bearded pink” name.

Ensuring sweet William has moist but well-drained soil is crucial for healthy and abundant bloom production. Overly hot temperatures also impact flowering capabilities. Deadheading spent flowers will also encourage more blooms. However, stop deadheading in the late summer to encourage self-seeding for new plants the following year.

IV. Uses and Benefits 

Flowers are used as a garnish for vegetable and fruit salads, cakes, sweets, iced tea and sorbet. They are also edible and have a moderate flavour. 

Ice cream, sorbet, salads, fruit salads, dessert sauces, shellfish, and stir-fries will all taste zestier with the addition of Sweet William petals.

Dianthus Barbatus are widely planted as border plants or as container plants due to their ornamental value to beautify home gardens. 

Dianthus Barbatus produces nectar that attracts bees, birds, moths, and butterflies.

Dianthus Barbatus flowers make an incredible addition to wedding bouquets, table centerpieces and other kinds of flower arrangements.

Sweet William (Dianthus barbatus) Details

Common name Sweet John, Sweet William
Botanical name Dianthus barbatus
Plant type Annual
Hardiness zone 3a, 3b, 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a, 8b, 9a, 9b
Growth rate Medium
Height 1 ft. 0 in. - 2 ft. 0 in.
Width 1 ft. 0 in. - 2 ft. 0 in.
Sunlight Full sun (6 or more hours of direct sunlight a day)
Soil condition High Organic Matter
Flower color Pink
Leaf color Blue