When does tall evening primrose bloom in California?

Most often in May. Across 601 dated, research-grade observations of Oenothera elata in California, the flowering season runs roughly January to December.

Peak May In flower 601 Examined 631 State California

Flowering 601 in flower of 631 examined

94%

88%

81%

82%

100%

95%

98%

96%

100%

93%

96%

Proportion of examined Oenothera elata in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	16	17	94%	73% to 99%
Feb	23	26	88%	71% to 96%
Mar	21	26	81%	62% to 91%
Apr	23	28	82%	64% to 92%
May	55	55	100%	93% to 100%
Jun	99	104	95%	89% to 98%
Jul	128	130	98%	95% to 100%
Aug	55	57	96%	88% to 99%
Sep	53	53	100%	93% to 100%
Oct	53	57	93%	83% to 97%
Nov	48	50	96%	87% to 99%
Dec	27	28	96%	82% to 99%

Peak flowering in May. Each bar is the share of Oenothera elata in California observations in which someone actually recorded the reproductive state and found the plant in flower, not the raw number of flowering records. That distinction matters: people observe plants far more in spring than in winter, so a bare count of flowering records partly measures when people go outside. Dividing by the number examined removes that. 601 of 631 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. This is still a global aggregate and not a forecast for your garden: the same species flowers on different dates in different hemispheres. Where a species has fewer than 30 flowering records we do not draw this chart at all. Computed from 10.15468/dl.wt38fd.

What this is, and what it is not

This is a record of when people in California found Oenothera elata in flower, not a forecast. It is computed only from observations made in California, so it is not the species’ global average dragged onto a map: the same plant flowers on different dates in different places, and that is the entire point of the page.

It will not tell you what your particular plant will do this year. Bloom time moves with the season, with altitude, and with the weather, and a warm February pulls everything forward. We publish the distribution and the sample size, and we refuse to draw a month that too few people examined.

The plant

Oenothera elata

tall evening primrose

Sourcesevery claim on this page

GBIF (iNaturalist Research-grade Observations). Dated flowering annotations in California. Every record achieved iNaturalist quality grade Research, which is applied upstream at export. 10.15468/dl.wt38fd. Retrieved 2026-07-14.
World Flora Online Plant List. The accepted name. CC0. Retrieved 2026-07-12.