Illustration
Sylvia
Dahlia 'Sylvia'
Sylvia blooms from July through October.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Sylvia
Plant it in full sun. It prefers high water. It is hardy in USDA zones 8–10. Expect it to reach about 3 ft tall and 1.5 ft wide at maturity, in roughly 1 year (a house reading).
Is Sylvia toxic to dogs or cats?
- Listed as toxic to dogs and cats by NC State Extension.
- 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 Sylvia
Sylvia is tender: plant it out after the last frost, once the soil has warmed. In zone 9, the middle of its hardy zones 8 to 10, that means February or March; where spring comes later, it goes out later. Expect flowers from July to October.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 9, the middle of this plant's hardy range, start with zone 9 in February. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Sylvia get?
3 fttall5 ft 7 inan adult1.5 ftwideSee Sylvia in a garden plan: the planner shows it in 3D beside everything else you add, growing toward this size over the years.
Where these facts come from
Sylvia's height, spread, hardiness zones, sun, water, bloom months and color and trait tags were checked against 5 published sources on October 21, 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.
- whiteflowerfarm.comWhite Flower Farmheight, spread, hardiness zones, sun, bloom months and color and trait tags
- RHSRoyal Horticultural Societyheight, sun, water, bloom months and color and trait tags
- promessedefleurs.iePromesse de Fleursheight, spread, hardiness zones and bloom months and color
- fleurfarm.comFleur Farmheight, sun and bloom months and color
- ashridgetrees.co.ukAshridgebloom months and color
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Sylvia
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
Toxic to dogs, cats and horses, causing mild stomach upset and mild dermatitis. The leaves and tubers can also irritate skin, worse with sun exposure. per ASPCA and NC State
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Design a garden with this
Drop this plant onto a 3D plan, see how it fills in, and watch your whole garden bloom across the year.