When does common yarrow bloom in California?

Most often in July. Across 2,600 dated, research-grade observations of Achillea millefolium in California, the flowering season runs roughly April to September.

Peak July In flower 2,600 Examined 3,537 State California

Flowering 2,600 in flower of 3,537 examined

24%

33%

43%

75%

90%

91%

88%

83%

62%

38%

34%

Proportion of examined Achillea millefolium in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	26	110	24%	17% to 32%
Feb	58	176	33%	26% to 40%
Mar	149	350	43%	38% to 48%
Apr	744	986	75%	73% to 78%
May	674	746	90%	88% to 92%
Jun	378	414	91%	88% to 94%
Jul	278	304	91%	88% to 94%
Aug	113	128	88%	82% to 93%
Sep	82	99	83%	74% to 89%
Oct	41	66	62%	50% to 73%
Nov	33	87	38%	28% to 48%
Dec	24	71	34%	24% to 45%

Peak flowering in Jul. Each bar is the share of Achillea millefolium 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. 2,600 of 3,537 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 Achillea millefolium 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

Achillea millefolium

common yarrow

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.