Evening Primrose (Oenothera biennis)

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Sunlight Full sun to partial shade; performs best in unobstructed sunlight for most of the day

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Watering Allow top 5–7 cm of soil to dry completely between waterings; drought-tolerant once fully established

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Temperature Hardy to USDA zone 4; withstands freezing winters and hot, dry summer conditions

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Leaf: First-year basal rosette of lanceolate, pubescent leaves; second-year stem leaves are alternate, toothed, and hairy
Flower: Bright yellow, four-petaled blooms that open in late afternoon and close by mid-morning
Stem: Erect, hairy, branching upper stem in second year of growth

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Watering

Water regularly until established; reduce watering frequency once mature plants develop deep roots

Fertilization

Light, balanced feed once monthly. Avoid over-fertilization to prevent excessive foliage growth at the expense of blooms

Composted eggshell powder：Sprinkle a thin layer around base of plants in early spring to support stem strength and bloom development

Pruning

Deadhead spent blooms regularly to encourage prolonged flowering through late summer
Cut back all foliage to ground level after first hard frost in autumn to prepare for winter dormancy
Thin overcrowded basal rosettes in early spring to improve airflow and reduce disease risk

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Warning: this plant may be toxic.

Pets & Humans

Pets: ASPCA-verified non-toxic to cats

Humans: Non-toxic to humans; seeds are commercially used for evening primrose oil supplements

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Culture: N/A

Usage: Ornamental wildflower; seeds harvested for evening primrose oil used in dietary supplements