Cosmos
Cosmos bipinnatus
Cosmos is the airy, ferny-leaved cottage annual that fills a garden bed with pink, magenta, white, or cream daisies on slender 90 to 150 cm stems from late July through hard frost. Native to Mexico and a top-tier pollinator plant: bumble bees, honey bees, native solitary bees, butterflies, and goldfinches all use it. The classic Sensation series ('Sensation Mix', 'Sensation White Purity', 'Sensation Pink') is tall and full-season; the Sonata series is compact (60 cm) for smaller beds; the Bright Lights series gives orange and yellow flowers on slightly different species (Cosmos sulphureus). One of the easiest annuals from seed: direct-sow after last frost and the plants take care of themselves through the entire season. The most common mistake is over-fertilizing, which produces lush foliage and very few flowers; cosmos genuinely prefers lean soil. Tall varieties may need staking or peony rings in windy Edmonton yards; alternatively, pinch the central growing tip at 30 cm tall to force a shorter, bushier plant.
Quick Facts
Distribution
Summer annual across Alberta. Native to Mexico.
Light
Full sun.
Bloom Time
Late July through hard frost
Soil
Lean to average, well-drained. Rich soil reduces flowering.
Water
Low to moderate. Drought-tolerant once established.
Growing & Cultivation
Best Planting Time
Direct-sow late May after frost risk. Germinates in 7 to 10 days at 18 to 21 C.
Propagation
Direct seed 5 mm deep, 30 cm apart. Self-seeds modestly in Edmonton if pods are left to mature.
Pruning / Splitting
Pinch growing tips at 30 cm for a bushier plant. Deadhead spent flowers to extend bloom and reduce self-seeding (or leave some seed for goldfinches and next year's volunteers).
Seed Collection
Pods mature dry on the plant in September. Strip ripe seed (long, thin, brown) by hand and store in a paper envelope. Germination remains strong for 3 to 4 years.
Spacing
30 to 45 cm.
