When does Asian mustard bloom in California?

Most often in February. Across 652 dated, research-grade observations of Brassica tournefortii in California, the flowering season runs roughly February to March.

Peak February In flower 652 Examined 1,250 State California

Flowering 652 in flower of 1,250 examined

44%

66%

59%

33%

21%

20%

42%

Proportion of examined Brassica tournefortii in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	179	408	44%	39% to 49%
Feb	248	378	66%	61% to 70%
Mar	176	300	59%	53% to 64%
Apr	27	83	33%	23% to 43%
May	4	19	21%	9% to 43%
Jun	1	2	too few examined
Jul	1	1	too few examined
Aug	0	2	too few examined
Sep	0	2	too few examined
Oct	0	12	0%	0% to 24%
Nov	2	10	20%	6% to 51%
Dec	14	33	42%	27% to 59%

Peak flowering in Feb. Each bar is the share of Brassica tournefortii 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. 652 of 1,250 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 4 months have fewer than 5 examined observations, so no proportion is drawn for them. 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 Brassica tournefortii 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

Brassica tournefortii

Asian mustard

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.