Illustration
Formosa
Rhododendron 'Formosa'
Formosa blooms from April through May.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Formosa
Plant it in part shade. It prefers moderate water. It is hardy in USDA zones 7–9. Expect it to reach about 6 ft tall and 5 ft wide at maturity, in roughly 4 years (a house reading).
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 Formosa
Plant Formosa 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 8, the middle of its hardy zones 7 to 9, spring means February to April and fall means September or October. Once settled, it blooms from April to May.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 8, the middle of this plant's hardy range, start with zone 8 in February. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Formosa get?
6 fttall5 ft 7 inan adult5 ftwideSee Formosa 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 Formosa
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Formosa about 5 ft apart, center to center, so each plant has room to reach its full width.
Add Formosa 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
Formosa's height, spread, hardiness zones, sun, water, bloom months and color, trait tags, soil, diseases, pests and toxicity were checked against 9 published sources on August 24, 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.
- University of Georgia ExtensionUniversity of Georgia Cooperative Extension (CAES), Bulletin 670height, spread, hardiness zones, sun, water, bloom months and color, trait tags, soil, diseases and pests
- NC State ExtensionPlant Toolboxspread, hardiness zones, sun, water, bloom months and color, soil, diseases, pests and toxicity
- aces.eduAlabama Cooperative Extension System (Auburn University and Alabama A&M)height, hardiness zones, sun, water, bloom months and color, soil, diseases and pests
- wilsonbrosgardens.comWilson Bros Gardensheight, spread, hardiness zones, sun, water, bloom months and color, trait tags and soil
- NC State ExtensionPlant Toolbox, Rhododendron Southern Indica Hybridsheight, spread, hardiness zones, sun, bloom months and color, soil and pests
- rhododendron.orgAmerican Rhododendron Society, Azalea Plant Databaseheight, hardiness zones, sun and bloom months and color
- University of Florida IFASGardening Solutionshardiness zones, sun, bloom months and color and trait tags
- azaleas.orgAzalea Society of Americabloom months and color
- ASPCAAnimal Poison Controltoxicity
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Formosa
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
All parts contain grayanotoxins. Toxic to dogs, cats and horses: vomiting, diarrhea, weakness, and in serious cases cardiac failure. Pets and livestock are poisoned more readily than people. 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.