When does prickly sowthistle bloom in California?

Most often in April. Across 148 dated, research-grade observations of Sonchus asper in California, the flowering season runs roughly February to December.

Peak April In flower 148 Examined 273 State California

Flowering 148 in flower of 273 examined

39%

55%

60%

67%

50%

56%

17%

29%

33%

42%

50%

63%

Proportion of examined Sonchus asper in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	12	31	39%	24% to 56%
Feb	11	20	55%	34% to 74%
Mar	28	47	60%	45% to 72%
Apr	52	78	67%	56% to 76%
May	14	28	50%	33% to 67%
Jun	5	9	56%	27% to 81%
Jul	1	6	17%	3% to 56%
Aug	2	7	29%	8% to 64%
Sep	3	9	33%	12% to 65%
Oct	5	12	42%	19% to 68%
Nov	5	10	50%	24% to 76%
Dec	10	16	63%	39% to 82%

Peak flowering in Apr. Each bar is the share of Sonchus asper 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. 148 of 273 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 asper 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 asper

prickly sowthistle

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.