When does Petty Spurge bloom in California?

Most often in April. Across 256 dated, research-grade observations of Euphorbia peplus in California, the flowering season runs roughly February to November.

Peak April In flower 256 Examined 465 State California

Flowering 256 in flower of 465 examined

40%

75%

78%

82%

58%

50%

72%

62%

40%

71%

18%

Proportion of examined Euphorbia peplus in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	44	111	40%	31% to 49%
Feb	24	32	75%	58% to 87%
Mar	35	45	78%	64% to 87%
Apr	58	71	82%	71% to 89%
May	11	19	58%	36% to 77%
Jun	10	20	50%	30% to 70%
Jul	23	32	72%	55% to 84%
Aug	1	2	too few examined
Sep	28	45	62%	48% to 75%
Oct	4	10	40%	17% to 69%
Nov	5	7	71%	36% to 92%
Dec	13	71	18%	11% to 29%

Peak flowering in Apr. Each bar is the share of Euphorbia peplus 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. 256 of 465 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. One month has fewer than 5 examined observations, so no proportion is drawn for it. 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 Euphorbia peplus 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

Euphorbia peplus

Petty Spurge

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.