Illustration
Astra Double Blue
Platycodon grandiflorus 'Astra Double Blue'
Astra Double Blue blooms from July through August.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Astra Double Blue
Plant it in full sun. It prefers moderate water. It is hardy in USDA zones 3–8. Expect it to reach about 10 in tall and 12 in wide at maturity, in roughly 2 years (a house reading).
No toxicity note is on file for Astra Double Blue. That is not a clearance: check its safety for people and pets before planting.
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 Astra Double Blue
Plant Astra Double Blue 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 5, the middle of its hardy zones 3 to 8, spring means April to June and fall means August or September. Once settled, it blooms from July to August.
Month-by-month timing for your zone is on the planting calendar; if you garden near zone 5, the middle of this plant's hardy range, start with zone 5 in April. Derived from the plant's category, zones and bloom months plus typical zone frost dates, not checked separately.
How big does Astra Double Blue get?
10 intall5 ft 7 inan adult12 inwideSee Astra Double Blue 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 Astra Double Blue
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Astra Double Blue about 12 in apart, center to center, so each plant has room to reach its full width.
Add Astra Double Blue 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
Astra Double Blue'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.
- Perennial Resource (Walters Gardens)Walters Gardens (Perennial Resource)height, hardiness zones, sun, water, bloom months and color, trait tags, soil, diseases and pests
- Plant Addictsheight, hardiness zones, water, bloom months and color, soil and pests
- Chicago Botanic GardenPlant Finderhardiness zones, sun, bloom months and color and pests
- Missouri Botanical GardenPlant Findersun, water, soil, diseases and pests
- plants.tedsgardens.comNetPS Plant Finder (syndicated; read at plants.tedsgardens.com)spread, sun, water, soil and diseases
- University of Illinois Extensionsun, water, bloom months and color and soil
- NC State ExtensionPlant Toolboxsun, soil and pests
- Plants For A Futuretoxicity
- Swallowtail Garden Seedspests
How the checking works, and what each standard covers, is on the verified plants page.
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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.