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Oenothera biennis

Common Evening Primrose · Evening Primose · Evening Primrose · German Rampion

Family OnagraceaeGenus Oenothera

Bright yellow four-petalled flowers opening from a crowded head of red-green buds on a stout leafy stem, in meadow grass.
FlowerChristian FerrerCC BY-SA 4.0

About the plant

What it is and where it grows — not part of any germination protocol.

The plant

Habit
Herbaceous perennialPlant Finder
Habit
biennialPlants of the World Online
Height
3-5 ft0.9-1.5 mPlant Finder
Spread
2-3 ft60-90 cmPlant Finder
Flower
Showy; yellowPlant Finder
Blooms
June to SeptemberPlant Finder
Native range
Eastern North AmericaPlant Finder
Hardiness zones
4-9Plant Finder
Note
Attracts birds and butterflies. Tolerates drought.Plant Finder

Growing conditions

Sun
Full sun to part shadePlant Finder
Soil
Average, medium moisture, well-drainedPlant Finder
Soil pH
Acid (<6.0), Neutral (6.0-8.0)Extension Gardener Plant Toolbox
Moisture
Good Drainage, Occasionally DryExtension Gardener Plant Toolbox
Watering
MediumPlant Finder

Toxicity is noted only where a source states it. No note here is not a finding of safety.

Sources: Plant Finder — Missouri Botanical Garden; Plants of the World Online — Royal Botanic Gardens, Kew; Extension Gardener Plant Toolbox — NC State Extension.

Worth knowing

This source reports 10 treatments. All are shown.

Protocol 1

DerivedN. C. Deno, 1993

Difficulty Low Rated by us, not by the source.

Start around June 19, 2027 for a May 3 last frost. Too late for spring 2027 — that needed starting on June 18, 2026.

  1. Dry storage

    Duration: 180 daysTemperature: 70°F 21°C

    Deno got the same from six months at 40.

  2. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

    Deno gives no length for this period; three months is his standard cycle.

  3. Sow on the surface — do not cover

    Temperature: 70°F 21°C Light: light

about 9 months from start to sowing. Germination time not stated; 21 days assumed.

90% germination.

90-95%, the best route: six months dry, a cold period, then light.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, OenotheraPublic domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis has an absolute light requirement so that photorequirements have to be considered in this genus. 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 2

DerivedN. C. Deno, 1993

Difficulty Moderate Rated by us, not by the source.

Start around June 19, 2027 for a May 3 last frost. Too late for spring 2027 — that needed starting on June 18, 2026.

  1. Dry storage

    Duration: 180 days

  2. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

  3. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C Light: light

about 9 months from start to step 3. Germination happens during step 3; time not stated, 21 days assumed.

90% germination.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Oenothera p. 181Public domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera p. 181. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 3

DerivedN. C. Deno, 1993

Difficulty Low Rated by us, not by the source.

Start around January 2, 2027 for a May 3 last frost.

  1. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

    Deno gives no length for this period; three months is his standard cycle.

  2. Sow on the surface — do not cover

    Temperature: 70°F 21°C Light: light

about 3 months from start to sowing. Then 3 days to germinate.

85% germination in 2–3 days.

Fresh seed, cold first, then light: 85% inside three days of the move.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, OenotheraPublic domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis has an absolute light requirement so that photorequirements have to be considered in this genus. 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 4

DerivedN. C. Deno, 1993

Difficulty Moderate Rated by us, not by the source.

Start around January 2, 2027 for a May 3 last frost.

  1. Cold moist stratification

    Duration: 90 daysTemperature: 40°F 4°C

  2. Warm moist stratification

    Duration: 90 daysTemperature: 70°F 21°C Light: light

about 3 months from start to step 2. Germination happens during step 2, in 3 days.

85% germination in 2–3 days.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Oenothera p. 181Public domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera p. 181. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 5

DerivedN. C. Deno, 1993

Difficulty Low Rated by us, not by the source.

Start around September 17, 2027 for a May 3 last frost. Too late for spring 2027 — that needed starting on September 16, 2026.

  1. Dry storage

    Duration: 180 daysTemperature: 70°F 21°C

  2. Sow on the surface — do not cover

    Temperature: 70°F 21°C Light: light

about 6 months from start to sowing. Germination time not stated; 21 days assumed.

60% germination.

60-75% with no cold period at all, if the seed has been stored six months.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, OenotheraPublic domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis has an absolute light requirement so that photorequirements have to be considered in this genus. 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 6

DerivedN. C. Deno, 1993

Difficulty Moderate Rated by us, not by the source.

Start around September 17, 2027 for a May 3 last frost. Too late for spring 2027 — that needed starting on September 16, 2026.

  1. Dry storage

    Duration: 180 days

  2. Sow and cover

    Temperature: 70°F 21°C Light: light

about 6 months from start to sowing. Germination time not stated; 21 days assumed.

60% germination.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Oenothera p. 181Public domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera p. 181. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 7

DerivedN. C. Deno, 1993

Difficulty Low Rated by us, not by the source.

Start around March 22, 2027 for a May 3 last frost.

  1. Sow on the surface — do not cover

    Temperature: 70°F 21°C Light: light

No stated waiting before sowing. Then 14 days to germinate.

55% germination in 14 days.

The simplest route. Light is not optional: everything without it stayed under 2%.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, OenotheraPublic domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis has an absolute light requirement so that photorequirements have to be considered in this genus. 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 8

DerivedN. C. Deno, 1993

Difficulty Moderate Rated by us, not by the source.

Start around March 22, 2027 for a May 3 last frost.

  1. Sow and cover

    Temperature: 70°F 21°C Light: light

No stated waiting before sowing. Then 14 days to germinate.

55% germination in 14 days.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Oenothera p. 181Public domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera p. 181. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 9

DerivedN. C. Deno, 1993

Difficulty Moderate Rated by us, not by the source.

Start around March 1, 2027 for a May 3 last frost.

  1. Gibberellic acid soak

  2. Sow and cover

    Temperature: 70°F 21°C Light: dark

No stated waiting before sowing. Then 35 days to germinate.

50% germination in 7–35 days.

GA-3 is the only substitute for light that Deno found working here.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, OenotheraPublic domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis has an absolute light requirement so that photorequirements have to be considered in this genus. 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

Protocol 10

DerivedN. C. Deno, 1993

Difficulty Moderate Rated by us, not by the source.

Start around March 1, 2027 for a May 3 last frost.

  1. Gibberellic acid soak

  2. Sow and cover

    Temperature: 70°F 21°C Light: dark

No stated waiting before sowing. Then 35 days to germinate.

50% germination in 7–35 days.

Seed Germination Theory and Practice, 2nd ed. — N. C. Deno, 1993 · Ch. 20, Oenothera p. 181Public domain
Show the original text
Oenothera (Onagraceae). While many species germ. well in dark treatments, 0. biennis requires light or GA-3 for germination. The data for fresh seeds were 70L(55% in 2nd w), 70D GA-3(50% in 1-5 w), and 40-70L(85% in 2-3 d). The data for seeds DS 6 m at 40 or 70 were 70L(60-75%) and 40-70L(90-95%). Germination in all other treatments never exceeded 2%.
Seed Germination Theory and Practice, 2nd ed., Ch. 20, Oenothera p. 181. Quoted exactly. Every value on this card comes from this record, except the difficulty rating, which is ours; the step names come from a fixed list.

How each step is done, in Deno’s words, and what Verified and Derived mean.

Germination trials

Readers’ own records of sowing this species, published after review. Share your trial · All trials

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