When does California mugwort bloom in California?

Most often in September. Across 254 dated, research-grade observations of Artemisia douglasiana in California, the flowering season runs roughly August to September.

Peak September In flower 254 Examined 1,051 State California

Flowering 254 in flower of 1,051 examined

40%

65%

67%

25%

21%

Proportion of examined Artemisia douglasiana in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	49	0%	0% to 7%
Feb	1	52	2%	0% to 10%
Mar	0	110	0%	0% to 3%
Apr	0	117	0%	0% to 3%
May	1	83	1%	0% to 7%
Jun	12	137	9%	5% to 15%
Jul	64	159	40%	33% to 48%
Aug	91	141	65%	56% to 72%
Sep	69	103	67%	57% to 75%
Oct	10	40	25%	14% to 40%
Nov	6	28	21%	10% to 40%
Dec	0	32	0%	0% to 11%

Peak flowering in Sep. Each bar is the share of Artemisia douglasiana 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. 254 of 1,051 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 Artemisia douglasiana 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

Artemisia douglasiana

California mugwort

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.