When does Common Sunflower bloom in California?

Most often in August. Across 283 dated, research-grade observations of Helianthus annuus in California, the flowering season runs roughly January to December.

Peak August In flower 283 Examined 307 State California

Flowering 283 in flower of 307 examined

85%

94%

81%

89%

87%

91%

100%

91%

96%

100%

Proportion of examined Helianthus annuus in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	22	26	85%	66% to 94%
Feb	15	16	94%	72% to 99%
Mar	13	16	81%	57% to 93%
Apr	25	28	89%	73% to 96%
May	27	31	87%	71% to 95%
Jun	29	32	91%	76% to 97%
Jul	29	32	91%	76% to 97%
Aug	37	37	100%	91% to 100%
Sep	28	28	100%	88% to 100%
Oct	20	22	91%	72% to 97%
Nov	23	24	96%	80% to 99%
Dec	15	15	100%	80% to 100%

Peak flowering in Aug. Each bar is the share of Helianthus annuus 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. 283 of 307 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 Helianthus annuus 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

Helianthus annuus

Common Sunflower

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.