When does stinging phacelia bloom in California?

Most often in August. Across 220 dated, research-grade observations of Phacelia malvifolia in California, the flowering season runs roughly April to August.

Peak August In flower 220 Examined 263 State California

Flowering 220 in flower of 263 examined

59%

85%

99%

98%

89%

100%

60%

Proportion of examined Phacelia malvifolia in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	5	0%	0% to 43%
Feb	0	10	0%	0% to 28%
Mar	10	17	59%	36% to 78%
Apr	44	52	85%	72% to 92%
May	86	87	99%	94% to 100%
Jun	54	55	98%	90% to 100%
Jul	16	18	89%	67% to 97%
Aug	6	6	100%	61% to 100%
Sep	3	5	60%	23% to 88%
Oct	1	2	too few examined
Nov	0	2	too few examined
Dec	0	4	too few examined

Peak flowering in Aug. Each bar is the share of Phacelia malvifolia 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. 220 of 263 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 3 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 Phacelia malvifolia 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

Phacelia malvifolia

stinging phacelia

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.