When does Grinnell's beardtongue bloom in California?

Most often in June. Across 443 dated, research-grade observations of Penstemon grinnellii in California, the flowering season runs roughly May to July.

Peak June In flower 443 Examined 551 State California

Flowering 443 in flower of 551 examined

65%

90%

95%

91%

63%

44%

33%

22%

Proportion of examined Penstemon grinnellii in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	9	0%	0% to 30%
Feb	0	4	too few examined
Mar	0	4	too few examined
Apr	15	23	65%	45% to 81%
May	74	82	90%	82% to 95%
Jun	176	186	95%	90% to 97%
Jul	126	139	91%	85% to 94%
Aug	33	52	63%	50% to 75%
Sep	14	32	44%	28% to 61%
Oct	3	9	33%	12% to 65%
Nov	2	9	22%	6% to 55%
Dec	0	2	too few examined

Peak flowering in Jun. Each bar is the share of Penstemon grinnellii 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. 443 of 551 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 Penstemon grinnellii 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

Penstemon grinnellii

Grinnell's beardtongue

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.