When does Pacific trillium bloom in California?

Most often in March. Across 3,080 dated, research-grade observations of Trillium ovatum in California, the flowering season runs roughly January to April.

Peak March In flower 3,080 Examined 3,943 State California

Flowering 3,080 in flower of 3,943 examined

90%

96%

81%

41%

Proportion of examined Trillium ovatum in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	46	51	90%	79% to 96%
Feb	748	783	96%	94% to 97%
Mar	1541	1610	96%	95% to 97%
Apr	592	734	81%	78% to 83%
May	122	296	41%	36% to 47%
Jun	20	220	9%	6% to 14%
Jul	5	124	4%	2% to 9%
Aug	1	51	2%	0% to 10%
Sep	3	38	8%	3% to 21%
Oct	1	18	6%	1% to 26%
Nov	1	14	7%	1% to 31%
Dec	0	4	too few examined

Peak flowering in Mar. Each bar is the share of Trillium ovatum 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. 3,080 of 3,943 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. One month has fewer than 5 examined observations, so no proportion is drawn for it. 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 Trillium ovatum 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

Trillium ovatum

Pacific trillium

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.