When does hairy yerba santa bloom in California?

Most often in May. Across 192 dated, research-grade observations of Eriodictyon trichocalyx in California, the flowering season runs roughly May to June.

Peak May In flower 192 Examined 511 State California

Flowering 192 in flower of 511 examined

17%

64%

87%

79%

61%

Proportion of examined Eriodictyon trichocalyx in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	33	0%	0% to 10%
Feb	0	43	0%	0% to 8%
Mar	16	92	17%	11% to 26%
Apr	67	104	64%	55% to 73%
May	62	71	87%	78% to 93%
Jun	30	38	79%	64% to 89%
Jul	17	28	61%	42% to 76%
Aug	0	20	0%	0% to 16%
Sep	0	14	0%	0% to 22%
Oct	0	24	0%	0% to 14%
Nov	0	24	0%	0% to 14%
Dec	0	20	0%	0% to 16%

Peak flowering in May. Each bar is the share of Eriodictyon trichocalyx 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. 192 of 511 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 Eriodictyon trichocalyx 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

Eriodictyon trichocalyx

hairy yerba santa

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.