Biennial or perennial
How to grow sweet williams
Dianthus barbatus
Sweet william is a hardy biennial: sow it one summer and it flowers the next. Sow outdoors in a seedbed from May to July, move the young plants to their flowering positions in September or October, 20 to 30 cm apart, and they bloom in June and July of the following year. Give them full sun and free-draining soil that is neutral or slightly alkaline. Winter wet on heavy ground is what loses plants; cold does not.
- Hardiness
- Fully hardy biennial
- Position
- Full sun
- Soil
- Free-draining, neutral to alkaline
- Ideal pH
- 6.5 to 7.5
- Water
- Low to moderate
- Feeding
- Light feeder
Sowing and planting sweet williams
WhenSow May to Jul; plant out Sep to Oct; flowers Jun to Jul the following year
Starting off
Sow May to Jul in a seedbed outdoors 5 mm deep, germination 7 to 14 days at 15 to 20 °C; thin to 10 cm and transplant to flowering positions Sep to Oct. A Feb sowing at 18 °C under glass flowers the same year for annual strains. Perennial forms root from 8 cm cuttings in Jul.
Spacing and planting
Plant 20 to 30 cm apart in a block; sow 5 mm deep in rows 20 cm apart. Fine in a 30 cm pot of gritty compost.
Varieties worth growing
- 'Auricula-Eyed Mixed'
- The traditional cottage strain: reds, pinks and whites, each floret with a contrasting ring; 45 cm and well scented.
- 'Sooty'
- Deep maroon, near-black flowers over dark-flushed leaves; striking in a vase with paler flowers.
- 'Albus'
- Pure white heads on 50 cm stems, good for cutting and for evening scent.
- 'Sweet' series F1
- Bred for cutting, with long 60 to 90 cm stems, and it will flower in its first summer from a February sowing under glass.
- 'Green Trick'
- A novelty with fuzzy green balls instead of petals, sold as young plants; grown purely as a long-lasting cut stem.
Sweet williams month by month
Timings are for central England. Allow two weeks later in the north and on cold, heavy soil.
- January
Nothing to do. Firm back any plants lifted by frost.
- February
Sow first-year-flowering strains under glass at 18 °C.
- March
Give the one light feed of the year. Weed between the plants.
- April
Water in a dry spell as the flower stems lengthen.
- May
Buds form. Start sowing next year's plants in a seedbed, 5 mm deep.
- June
Flowering. Cut for the house when a third of the florets on a head are open. Sow.
- July
Deadhead to side shoots. Last sowings early in the month. Thin seedlings to 10 cm.
- August
Pull spent plants, or cut to the rosette to try for a second year. Water the seedbed.
- September
Transplant young plants to their flowering positions and water in.
- October
Finish transplanting by the middle of the month so roots settle before winter.
- November
Nothing to do. Check that pigeons are not at the rosettes.
- December
Nothing to do.
Feeding sweet williams
A light feeder. One half-rate balanced feed in March of the flowering year is enough, and lime only if a pH test shows the soil is acid.
Low, a light feed; dianthus dislike rich, wet ground.
Feeding plan
Late winter or after the previous crop, acid soil only
Garden Lime (calcium carbonate)
Only if a test shows a pH below 6.5: up to 0.5 kg/m², the label rate for a typical bed, raked in well before the autumn planting. If the pH is 6.5 or above, none.
March of the flowering year, beds
50 g/m², half the label rate of about 100 g/m², scattered between the plants and hoed in: a generous handful per square metre. Once.
March of the flowering year, pots
2 g per litre of compost, the low end of the label top-dress: 24 g on the surface of a 30 cm pot holding 12 litres, watered in.
May, as buds form, optional
1 g per litre of water, the label rate, as a single drench at the base: 5 g in a 5 litre can.
Signs to watch
Leaves yellow on acid soil
Low pH
Lime to pH 6.5 to 7 in autumn
Lush leaves and poor flowers
Excess nitrogen
No feed
Stems collapse at the base in Feb
Winter wet rot, not nutrition
Grit and raised beds
Pests, diseases and problems
Small brown pustules in rings under the leaves, pale spots above, leaves wither
Sweet william rust, a fungus that is worst in damp, crowded plantings
Pick off affected leaves at the first sign, give plants the full 20 to 30 cm, and water at the base. Bin badly affected plants rather than keeping them for a second year, and grow next year's batch elsewhere.
Seedlings and young rosettes grazed, with slime trails
Slugs and snails
Keep the seedbed weeded and open, check at dusk, and use nematodes on moist soil in late summer.
Overwintering rosettes pecked or bitten down to the crown
Pigeons or rabbits
Net or cover with wire mesh from planting until growth takes off in April.
Leaves at the shoot tip bound together with silk, a small green caterpillar inside
Carnation tortrix moth
Squeeze the bound leaves to crush the caterpillar, or pick them off.
Flower stems sticky and stunted, with colonies of green insects
Aphids
Rub them off or wash them away with a jet of water before the buds open.
Pruning
Pruning and care
Deadhead the main heads to the side shoots for a second flush in Jul to Aug. Cut spent stems to the basal rosette in Aug; plants kept a second year flower again but weaker, so most growers pull them and resow. No staking; fully hardy, but winter wet on heavy soil rots them, so add grit.
Good to knowDeadhead for longer flowering; a good clove-scented cut flower.
Growing sweet williams in pots
Sweet williams grow well in a 30 cm pot, about 12 litres, of loam-based compost with a quarter of grit. Plant three or four young plants in September or October and stand the pot in full sun, raised on feet so it drains through winter. They need little water until growth starts in March, then watering whenever the top 2 cm is dry. After flowering the plants are finished, so empty the pot and replant; this suits a pot that holds tulips or wallflowers one year and sweet williams the next.
Sweet williams: common questions
When do you sow sweet william seeds?
Sow sweet william outdoors from May to early July for flowers the following summer. Sow thinly 5 mm deep in a seedbed, thin the seedlings to 10 cm, and move them to their final positions in September or October. Some modern F1 strains will flower the same year if sown under glass in February.
Do sweet williams come back every year?
Not reliably. Sweet william is a biennial that flowers in its second summer and then usually dies or flowers poorly. If you cut plants back to the rosette after flowering some will bloom again, but most gardeners sow a fresh batch each May so there are always plants coming on. It also self-seeds on light soil.
Are sweet williams good cut flowers?
Yes, they are among the best: clove-scented, strong-stemmed and lasting up to two weeks in water. Cut when about a third of the florets in the head are open, strip the lower leaves and stand the stems in deep water. Cutting also brings on side shoots for a second, smaller flush.
Sources
Growing information on this page was checked against these references in November 2026. Feeding rates are Dr Forest label rates.
- How to grow dianthusRHS
- Plants for kids: sweet williamsRHS
- How to grow and care for sweet williamBBC Gardeners' World