When does Coastal Goldenbush bloom in California?

Most often in October. Across 649 dated, research-grade observations of Isocoma menziesii in California, the flowering season runs roughly September to November.

Peak October In flower 649 Examined 849 State California

Flowering 649 in flower of 849 examined

72%

42%

44%

62%

63%

71%

73%

72%

90%

95%

85%

67%

Proportion of examined Isocoma menziesii in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	36	50	72%	58% to 83%
Feb	11	26	42%	26% to 61%
Mar	14	32	44%	28% to 61%
Apr	23	37	62%	46% to 76%
May	20	32	63%	45% to 77%
Jun	39	55	71%	58% to 81%
Jul	54	74	73%	62% to 82%
Aug	79	109	72%	63% to 80%
Sep	124	138	90%	84% to 94%
Oct	129	136	95%	90% to 97%
Nov	60	71	85%	74% to 91%
Dec	60	89	67%	57% to 76%

Peak flowering in Oct. Each bar is the share of Isocoma menziesii 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. 649 of 849 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 Isocoma menziesii 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

Isocoma menziesii

Coastal Goldenbush

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.