When does turkey mullein bloom in California?

Most often in September. Across 608 dated, research-grade observations of Croton setiger in California, the flowering season runs roughly July to September.

Peak September In flower 608 Examined 788 State California

Flowering 608 in flower of 788 examined

20%

29%

60%

63%

80%

94%

75%

44%

Proportion of examined Croton setiger in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	2	10	20%	6% to 51%
Feb	0	3	too few examined
Mar	1	5	20%	4% to 62%
Apr	7	24	29%	15% to 49%
May	18	30	60%	42% to 75%
Jun	67	107	63%	53% to 71%
Jul	138	172	80%	74% to 86%
Aug	150	160	94%	89% to 97%
Sep	152	162	94%	89% to 97%
Oct	54	72	75%	64% to 84%
Nov	12	27	44%	28% to 63%
Dec	7	16	44%	23% to 67%

Peak flowering in Sep. Each bar is the share of Croton setiger 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. 608 of 788 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 Croton setiger 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

Croton setiger

turkey mullein

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.