When does common yarrow bloom in Washington?

Most often in July. Across 634 dated, research-grade observations of Achillea millefolium in Washington, the flowering season runs roughly January to December.

Peak July In flower 634 Examined 853 State Washington

Flowering 634 in flower of 853 examined

76%

10%

20%

67%

86%

93%

91%

78%

61%

52%

79%

Proportion of examined Achillea millefolium in Washington in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	22	29	76%	58% to 88%
Feb	1	10	10%	2% to 40%
Mar	0	21	0%	0% to 15%
Apr	11	55	20%	12% to 32%
May	91	136	67%	59% to 74%
Jun	160	185	86%	81% to 91%
Jul	159	171	93%	88% to 96%
Aug	80	88	91%	83% to 95%
Sep	54	69	78%	67% to 86%
Oct	22	36	61%	45% to 75%
Nov	15	29	52%	34% to 69%
Dec	19	24	79%	60% to 91%

Peak flowering in Jul. Each bar is the share of Achillea millefolium in Washington 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. 634 of 853 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 Washington found Achillea millefolium in flower, not a forecast. It is computed only from observations made in Washington, 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 Washington. 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.