Plant of the Month July 2024
GENERAL INFORMATION: Oenothera belongs to the Onagraceae, or evening primrose family, native to N. & S. America. The genus has many delightful flowers, often night blooming, then fading in the morning light. The colours range from yellows, whites and pinks. Many are annuals or biennials and are often weedy. Oenothera triloba is a favourite plant as the flowers open rapidly at dusk, often in 2 minutes once started. O. flava is similar but slower to open.
Watch Oenothera triloba opening.
Video: Veronica Callinan.
Synonym: Lavauxia triloba, Oenothera hamata.
Oenothera triloba.
Common Name: Stemless Evening Primrose, Dandelion-leaved Evening Primrose.
Life Cycle: Stemless annual, or occasionally biennial. Winter annual in south US.
Range: Native to Southern US and Mexico.
Habitat: Dry open areas with well drained soil. Colonizes lawns in south.
Height: 20 cm.
Bloom Time: June through summer in Toronto.
Oenothera triloba - flower.
Flower Colour & Size: 4 bright yellow round petals, 5 cm long, with squared off ends, joined to form a long (up to 10 cm) floral tube. 8 stamens, 4 lobbed stigma, characteristic of Oenothera. 4 sepals, 2 cm long, usually remain attached at their tips. Opens in evening, fades to pale yellow, then dies in the morning. Dying flowers are light salmon coloured.
Fruit: Capsules, brown and hard when ripe, at soil level, 1-2 cm long, winged.
Oenothera triloba - developing capsule.
Leaves: Basal rosette of dandelion-like leaves, up to 20 cm long.
Oenothera triloba - leaves and flower buds.
CULTIVATION:
Plant: in pots, planters, edge of borders, even on a table so the opening flowers can be enjoyed in the evening.
Oenothera triloba - evening flowers. Image: Veronica Callinan.
Light: Full sun - will take some shade.
Soil: Well drained, neutral pH, sandy soil.
Water: Moderate.
USDA Hardiness: Zones 5-8.
Companion planting: Rock garden plants.
Propagation: By seed: Sow @ 20°C. Seed germinates within 3 months. Will self seed.
Pollinators: Moths.
Native Alternatives: Oenothera triloba is not native in Canada. Native Oenothera biennis is a tall, somewhat weedy, biennial Evening Primrose.
References:
https://plants.usda.gov/home/plantProfile?symbol=oetr2
https://fwbg.org/phytophilia-blog/what-is-this-thing-oenothera-triloba-fruit/
https://comalmg.org/focus-on-a-native-22
https://onrockgarden.com/index.php/germination-guide
Text and images supplied by Anna Leggatt (Toronto Master Gardener) and Veronica Callinan.