Illustration
Smooth Hydrangea
Hydrangea arborescens
Smooth Hydrangea blooms from June through September.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Smooth Hydrangea
Plant it in part shade. It prefers moderate water. It is hardy in USDA zones 3–9. Expect it to reach about 4 ft tall and 4 ft wide at maturity, in roughly 4 years (checked).
What was checked
Fifteen fields were checked against named botanical sources, each recorded beside the sources that carried it, with every unsettled point written down and decided: mature height and spread, hardiness zones, sun, water, bloom months and color, the trait tags, soil, diseases, pests, toxicity, the plant's own names, and years to mature size, which rests on a recorded house rule where no publisher states one and is marked so. 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 Smooth Hydrangea
Plant Smooth Hydrangea 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 June to September.
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 Smooth Hydrangea get?
4 fttall5 ft 7 inan adult4 ftwideSee Smooth Hydrangea 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 Smooth Hydrangea
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Smooth Hydrangea about 4 ft apart, center to center, so each plant has room to reach its full width.
Add Smooth Hydrangea 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
Smooth Hydrangea's height, spread, hardiness zones, sun, water, bloom months and color, years to mature size, trait tags, soil, diseases, pests and toxicity were checked against 8 published sources on August 15, 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 GardenPlant Finderheight, spread, hardiness zones, sun, water, bloom months and color, trait tags, diseases and pests
- NC State ExtensionPlant Toolboxheight, spread, hardiness zones, sun, bloom months and color, soil, diseases, pests and toxicity
- Lady Bird Johnson Wildflower Centerheight, sun, water, bloom months and color, years to mature size and soil
- The Morton Arboretumheight, spread, hardiness zones, sun, water, soil and diseases
- Chicago Botanic Gardenspread, hardiness zones, sun, bloom months and color and years to mature size
- toadshade.comToadshade Wildflower Farm (nursery)height, hardiness zones, bloom months and color and soil
- Mt. Cuba Centertrialbloom months and color, years to mature size and trait tags
- ASPCAtoxicity
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Smooth Hydrangea
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
Toxic to dogs, cats and horses; the leaves and buds hold a cyanogenic glycoside. Eating it mostly causes vomiting and diarrhea. per ASPCA
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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.