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Sweet William
Dianthus barbatus
Also comes in red, white and purple.
Sweet William blooms from May through July.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Sweet William
Plant it in full sun. It prefers moderate water. It is hardy in USDA zones 3–9. Expect it to reach about 16 in tall and 12 in wide at maturity, in roughly 2 years (a house reading).
Is Sweet William toxic to dogs or cats?
- Listed as toxic to dogs and cats by NC State Extension and Royal Horticultural Society.
- Listed as poisonous to people by NC State Extension.
Lists differ and none is complete. If a pet eats a plant and seems unwell, call a veterinarian or a pet poison helpline.
What was checked
Nine facts were checked against named botanical sources, each recorded beside the sources that carried it: mature height and spread, hardiness zones, sun, water, bloom months and color, the trait tags, and years to mature size, which rests on a recorded house rule where no publisher states one and is marked so. Soil, diseases, pests, toxicity and the plant's own names have not yet been read for this plant, and its trait tags are the ones a feature uses rather than every word a page prints. Each fact above carries its own mark. The planting, spacing and size sections are derived from these checked facts by a fixed rule, not checked separately, and the plant type is the library's own classification.
When to plant Sweet William
Plant Sweet William in early spring as soon as the soil is workable, or in early fall at least six weeks before your first frost, so roots establish in cool weather. In zone 6, the middle of its hardy zones 3 to 9, spring means March to May and fall means August or September. Once settled, it blooms from May to July.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 6, the middle of this plant's hardy range, start with zone 6 in March. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Sweet William get?
16 intall5 ft 7 inan adult12 inwideSee Sweet William in a garden plan: the planner shows it in 3D beside everything else you add, growing toward this size over the years.
How far apart to plant Sweet William
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Sweet William about 12 in apart, center to center, so each plant has room to reach its full width.
Add Sweet William to a garden plan and the planner draws it at its full width, so you see the spacing before you buy.
Where these facts come from
Sweet William's height, spread, hardiness zones, sun, water, bloom months and color and trait tags were checked against 7 published sources on October 20, 2026. Each one is linked below with every fact it carried, which can include a fact this page still marks as not yet checked, because a source carrying a value is not the same as the value being held to the standard. Facts not in that list, and the planting, spacing and size sections, are not covered by these sources.
- Missouri Botanical Gardenheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- NC State Extensionheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- olddairynursery.comThe Old Dairy Nursery & Gardensheight, spread, hardiness zones, sun, water, bloom months and color and trait tags
- American Meadowsheight, hardiness zones, sun and water
- RHSRoyal Horticultural Societyheight, sun and bloom months and color
- Native Plant Trust (Go Botany)Native Plant Trust, Go Botanyheight and bloom months and color
- Chicago Botanic Gardenhardiness zones
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Sweet William
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note. A note reports what its source says; where that differs from a fact above, the fact above is this entry's stored value, and its mark says whether it has been checked.
Safety
Mildly toxic to dogs and cats: an irritant causes mild stomach upset if eaten, and the foliage's saponins can give sensitive skin brief contact dermatitis. per ASPCA and NC State
Worth knowing
Often sold as a perennial, but it usually lives like a biennial: a leafy rosette the first year, flowers the second, then it fades. Resow to keep it going. per NC State and Clemson
Rabbit resistance is uncertain
NC State's species page calls it rabbit resistant, but its genus page says rabbits will browse it. Deer resistance is solid; do not count on rabbit protection. per NC State
Wet soil is the killer
Its top failure mode is crown and root rot in soggy ground, and the same wet conditions bring on rust. Sharp drainage and spacing for airflow prevent both. per NC State and UC IPM
Fragrant but deer resistant
The same pungent, sharp-tasting foliage that deters deer carries the fragrance and nectar that draw bees and butterflies. Its scent works for you two ways. per NC State
The name means bearded
The species name 'barbatus' means bearded, for the fringed, whiskery look of the frilled petals and the bracts beneath each flower cluster. per NC State
A cottage cutting-garden staple
The long-stemmed, flat-topped flower clusters are a cottage-garden cutting staple; cut them from a dedicated patch as the blooms open. per NC State
What pairs well with Sweet William
Good companions share its growing conditions and add something it lacks: an earlier or later bloom, a lower carpet in front, or structure through winter.
Perennial Sunflower
Shares full sun and moderate water; blooms in late summer as this one finishes; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Goldenrod
Shares full sun and low to moderate water; blooms in late summer as this one finishes; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Ironweed
Shares full sun and moderate water; blooms in late summer as this one finishes; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Switchgrass
Shares full sun and low to moderate water; blooms in late summer as this one finishes; both offer pollinator forage, in different months; its seed heads stand through winter, for structure and the birds.
Pampas Grass
Shares full sun and low to moderate water; blooms in late summer as this one finishes; its seed heads stand through winter, for structure and the birds; stands well above at 8 ft, a canopy to plant beneath.
Little Bluestem
Shares full sun and low to moderate water; blooms in late summer as this one finishes; its seed heads stand through winter, for structure and the birds; taller at 3.5 ft, for the layer behind it.
Love-Lies-Bleeding
Shares full sun and moderate water; overlaps, then carries the display into mid fall; both offer pollinator forage; taller at 3.5 ft, for the layer behind it.
Winterberry
Shares full sun and moderate to high water; blooms in mid fall, extending the bed's season; both offer pollinator forage, in different months; taller at 6.5 ft, for the layer behind it.
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Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.