When does Common Sow-thistle bloom in California?

Most often in October. Across 306 dated, research-grade observations of Sonchus oleraceus in California, the flowering season runs roughly March to December.

Peak October In flower 306 Examined 397 State California

Flowering 306 in flower of 397 examined

64%

78%

81%

79%

85%

48%

57%

91%

73%

100%

86%

81%

Proportion of examined Sonchus oleraceus in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	29	45	64%	50% to 77%
Feb	43	55	78%	66% to 87%
Mar	65	80	81%	71% to 88%
Apr	75	95	79%	70% to 86%
May	23	27	85%	68% to 94%
Jun	10	21	48%	28% to 68%
Jul	4	7	57%	25% to 84%
Aug	10	11	91%	62% to 98%
Sep	8	11	73%	43% to 90%
Oct	10	10	100%	72% to 100%
Nov	12	14	86%	60% to 96%
Dec	17	21	81%	60% to 92%

Peak flowering in Oct. Each bar is the share of Sonchus oleraceus 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. 306 of 397 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 Sonchus oleraceus 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

Sonchus oleraceus

Common Sow-thistle

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.