When does bristly oxtongue bloom in California?

Most often in September. Across 605 dated, research-grade observations of Helminthotheca echioides in California, the flowering season runs roughly June to November.

Peak September In flower 605 Examined 877 State California

Flowering 605 in flower of 877 examined

61%

52%

39%

55%

75%

84%

82%

89%

78%

75%

59%

Proportion of examined Helminthotheca echioides in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	27	44	61%	47% to 74%
Feb	14	27	52%	34% to 69%
Mar	16	31	52%	35% to 68%
Apr	33	84	39%	30% to 50%
May	63	115	55%	46% to 64%
Jun	80	106	75%	66% to 83%
Jul	86	102	84%	76% to 90%
Aug	60	73	82%	72% to 89%
Sep	76	85	89%	81% to 94%
Oct	61	78	78%	68% to 86%
Nov	53	71	75%	63% to 83%
Dec	36	61	59%	47% to 70%

Peak flowering in Sep. Each bar is the share of Helminthotheca echioides 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. 605 of 877 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 Helminthotheca echioides 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

Helminthotheca echioides

bristly oxtongue

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.