When does Herb Robert bloom in Oregon?

Most often in May. Across 697 dated, research-grade observations of Geranium robertianum in Oregon, the flowering season runs roughly May to July.

Peak May In flower 697 Examined 1,017 State Oregon

Flowering 697 in flower of 1,017 examined

47%

13%

26%

71%

92%

91%

76%

63%

61%

41%

40%

55%

Proportion of examined Geranium robertianum in Oregon in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	18	38	47%	32% to 63%
Feb	4	30	13%	5% to 30%
Mar	17	66	26%	17% to 37%
Apr	155	217	71%	65% to 77%
May	204	221	92%	88% to 95%
Jun	117	128	91%	85% to 95%
Jul	65	86	76%	66% to 83%
Aug	30	48	63%	48% to 75%
Sep	20	33	61%	44% to 75%
Oct	21	51	41%	29% to 55%
Nov	23	57	40%	29% to 53%
Dec	23	42	55%	40% to 69%

Peak flowering in May. Each bar is the share of Geranium robertianum in Oregon 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. 697 of 1,017 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 Oregon found Geranium robertianum in flower, not a forecast. It is computed only from observations made in Oregon, 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

Geranium robertianum

Herb Robert

Sourcesevery claim on this page

GBIF (iNaturalist Research-grade Observations). Dated flowering annotations in Oregon. 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.