Flowers

How to Grow Cornflower (Bachelor's Button): Planting, Spacing, Care & Bloom

Quick answer

Start indoors 6–8 weeks before last frost (NC State; ISU lists 8 weeks). In mild winter climates, seed outdoors in fall (NC). Alias: bachelor's button. Not perennial mountain bluet (C. montana).

Cornflower at a glance

PlantStart indoors: 8–6 wk before last frost
SunFull sun; tolerates poor soil and needs little fertilization (NC).
SpacingNC: height about 1–3 ft; width about 0.5–1 ft.
Days to bloomGAP (days); bloom season June-Oct. (Purdue HO-80)
-9-8-7-6-5-4-3-2-1LF+1+2+3
■ Start indoors   ■ Plant out   ■ Harvest
Weeks relative to last frost (LF). Colored weeks show when our ZIP planner schedules each step.
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Updated

Cornflower / bachelor's button (Centaurea cyanus) — hardy cool-season annual. Not perennial mountain bluet (C. montana).

Blue cornflower
Cornflower (Centaurea cyanus). Photo: Robert Flogaus-Faust, Wikimedia Commons, CC BY 4.0 (resized).

Sourced from university extension guides. For dates where you live, use the ZIP planting planner.

Planting timing

NC State: “Because it does better in cooler climates, seeds should be started indoors 6-8 weeks before last frost, or in mild winter climates can be seeded in situ directly outdoors in the fall.” (NC State Centaurea cyanus) Iowa State germination table: Bachelor's Button — 8 weeks sowing to planting. (ISU germination table) Purdue HO-14 lists 6 weeks as a lower bound. Planner: Start indoors last frost −8 to −6. Fall direct sow in mild climates is seasonal. NC handbook lists cornflower among hardy annuals that may also be spring-sown before last frost — no integer spring Direct sow weeks invented here.

Depth and spacing

NC: height about 1–3 ft; width about 0.5–1 ft. Thin for air circulation.

Sun, soil and water

Full sun; tolerates poor soil and needs little fertilization (NC). Well-drained site; cooler weather for best bloom.

Care

Cool-season annual — performance drops in summer heat. Deadhead for longer bloom / to limit reseeding. Stake taller plants in wind if needed.

Bloom

Typical bloom season about June–Oct (Purdue HO-80). Excellent cut flower; blue is classic, other colors exist.

Pests and diseases

NC: generally few serious problems; watch aphids and powdery mildew in crowded damp stands. Cultural spacing and air flow first.

Related: ZIP planner · organic pest control · poppies

Frequently asked questions

When do I start cornflower / bachelor's button?

Indoors 6–8 weeks before last frost (NC). Fall sow where winters are mild (NC).

Is bachelor's button the same plant?

Yes — Centaurea cyanus aliases include bachelor's button.

Same as mountain bluet?

No — perennial Centaurea montana is a different species.

Sources