Illustration
Millenium
Allium 'Millenium'
Also called ornamental onion and flowering onion
Millenium blooms from July through August.
Months here are Northern Hemisphere months; in the Southern Hemisphere, shift them by six months.
Growing Millenium
Plant it in full sun. It prefers low water. It is hardy in USDA zones 4–9. Expect it to reach about 18 in tall and 12 in wide at maturity, in roughly 2 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 Millenium
Plant Millenium 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 4 to 9, spring means March to May 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 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 Millenium get?
18 intall5 ft 7 inan adult12 inwideSee Millenium 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
Millenium'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 11 published sources on August 23, 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 GardenAllium 'Millenium'height, spread, hardiness zones, sun, water, bloom months and color, trait tags, soil, diseases and pests
- NC State ExtensionAllium 'Millenium'height, spread, hardiness zones, sun, bloom months and color, years to mature size, trait tags, soil, diseases and pests
- Walters GardensAllium 'Millenium'height, spread, hardiness zones, sun, water, bloom months and color, years to mature size, trait tags, soil and diseases
- kb.jniplants.comJohnson's Nursery Knowledgebase (Millenium Ornamental Onion)height, spread, hardiness zones, sun, water, bloom months and color, trait tags and pests
- New Moon NurseryAllium 'Millenium'height, spread, hardiness zones, sun, bloom months and color, years to mature size, trait tags and pests
- gertens.comGertens Garden Center (Allium, Ornamental Onion 'Millenium')height, spread, hardiness zones, sun, years to mature size, trait tags, soil and diseases
- Purdue ArboretumAllium 'Millenium'height, spread, sun, bloom months and color and trait tags
- usperennials.comUS Perennials (Ornamental Onion 'Millenium')height, spread, hardiness zones, sun, water and trait tags
- Proven WinnersMillenium Ornamental Onion, Allium hybridheight, spread, hardiness zones, sun and trait tags
- ASPCAToxic and Non-Toxic Plantstoxicity
- purdue.eduPurdue University Consumer Horticulture, relaying the Perennial Plant...hardiness zones
How the checking works, and what each standard covers, is on the verified plants page.
Good to know about Millenium
Curated from university extensions, botanic gardens and other primary sources, with the source named on every note.
Safety
Toxic to dogs, cats and horses: onion-family compounds damage red blood cells, causing Heinz-body hemolytic anemia. Cats are the most sensitive, and signs can lag days. per ASPCA and Merck
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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.