Oenothera pilosella aka Meadow Evening Primrose

Oenothera pilosella lives for more than two years. It belongs to Onagraceae, the evening primrose family. People call it prairie sundrops or evening primrose. Despite the latter name, its flowers open by day. It comes from the east-central and eastern United States. Missouri forms part of its native range. There, it grows in prairies and fields. It also grows in wet uplands and grassy places. It grows beside roads and along railway edges, too.

This plant forms a low, thick mat of leaf rosettes. These are leaves grouped close together at the base. Leafy stems grow straight up from this spreading mat. They bear narrow leaves shaped like a lance. Flower stems reach about 1–1.5 feet [0.30–0.46 metres] tall. Listed garden sizes reach 2 feet [0.61 metres] tall and wide. The plant covers the ground while flower stems rise above. Its shallow roots make unwanted plants fairly easy to pull. Still, its spread can cause problems in garden beds.

Bright yellow flowers grow in groups at the stem tips. Each has four petals and a broad, shallow shape. Flowers can span about 0.17 feet [0.05 metres]. The plant blooms from late spring to early summer. Chicago Botanic Garden lists bloom from May to June. Missouri Botanical Garden lists June to July. The plant does not bloom a second time. Club-shaped seed capsules form after the flowers fade. These seed cases reach about 0.08 feet [0.025 metres] long.

Prairie sundrops grows best in full sun. It also copes with light or partial shade. It grows in average soils with medium to wet moisture. Dry soil suits it, too, and it withstands some drought. It grows well in clay that is slightly acidic. It also copes with poor soil. This wide soil range gives gardeners a choice of planting sites. Both garden sources list USDA hardiness zones 3–8. Missouri Botanical Garden says it needs little care.

Plant it in groups at the front of a border. It suits cottage gardens, meadows, and native plant beds. Wild gardens and rain gardens are other places to use it. Its spread suits places where it can grow and spread freely. Leave room for that spread near other plants. Missouri Botanical Garden reports no serious problems with insects or disease.