Illustration
Blue Mirror
Delphinium grandiflorum 'Blue Mirror'
Blue Mirror blooms from June through August.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Blue Mirror
Plant it in full sun. It prefers moderate water. It is hardy in USDA zones 3–7. Expect it to reach about 16 in tall and 12 in wide at maturity, in roughly 2 years (a house reading).
Is Blue Mirror toxic to dogs or cats?
- Listed as toxic to dogs and cats by NC State Extension, Pet Poison Helpline and Royal Horticultural Society.
- Listed as poisonous to people by NC State Extension and Royal Horticultural Society.
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 Blue Mirror
Plant Blue Mirror 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 7, spring means April to June and fall means August or September. Once settled, it blooms from June 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 Blue Mirror get?
16 intall5 ft 7 inan adult12 inwideSee Blue Mirror 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 Blue Mirror
Derived from the mature spread above by a fixed rule, not checked separately: spacing is the spread, center to center.
Space Blue Mirror about 12 in apart, center to center, so each plant has room to reach its full width.
Add Blue Mirror 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
Blue Mirror's height, spread, hardiness zones, sun, water, bloom months and color and trait tags were checked against 8 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.
- Perennials.com (Heritage Perennials)Heritage Perennialsheight, spread, hardiness zones, sun, water and bloom months and color
- swiftgreenhouses.comSwift Greenhousesheight, spread, hardiness zones, sun and bloom months and color
- benary.comBenaryheight, sun, bloom months and color and trait tags
- gertens.comGertensheight, spread, hardiness zones and bloom months and color
- Chicago Botanic Gardenhardiness zones, sun and bloom months and color
- Missouri Botanical Gardensun and trait tags
- NC State Extensionsun and trait tags
- spl.cde.state.co.usColorado State Universityheight
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Blue Mirror
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
All parts are poisonous to people and pets; the diterpenoid alkaloids are most concentrated in young growth and seeds. NC State rates the poison severity High. 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.