When does California Aster bloom in California?

Most often in September. Across 1,385 dated, research-grade observations of Corethrogyne filaginifolia in California, the flowering season runs roughly January to December.

Peak September In flower 1,385 Examined 1,483 State California

Flowering 1,385 in flower of 1,483 examined

85%

91%

79%

58%

72%

84%

96%

99%

100%

99%

96%

98%

Proportion of examined Corethrogyne filaginifolia in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	55	65	85%	74% to 91%
Feb	53	58	91%	81% to 96%
Mar	41	52	79%	66% to 88%
Apr	35	60	58%	46% to 70%
May	44	61	72%	60% to 82%
Jun	72	86	84%	75% to 90%
Jul	162	168	96%	92% to 98%
Aug	267	269	99%	97% to 100%
Sep	271	272	100%	98% to 100%
Oct	189	190	99%	97% to 100%
Nov	106	110	96%	91% to 99%
Dec	90	92	98%	92% to 99%

Peak flowering in Sep. Each bar is the share of Corethrogyne filaginifolia 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. 1,385 of 1,483 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 Corethrogyne filaginifolia 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

Corethrogyne filaginifolia

California Aster

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.