When does Herb Robert bloom in Vermont?

Most often in November. Across 517 dated, research-grade observations of Geranium robertianum in Vermont, the flowering season runs roughly May to November.

Peak November In flower 517 Examined 569 State Vermont

Flowering 517 in flower of 569 examined

83%

99%

93%

97%

90%

96%

100%

Proportion of examined Geranium robertianum in Vermont in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	0	too few examined
Feb	0	0	too few examined
Mar	0	1	too few examined
Apr	0	12	0%	0% to 24%
May	95	114	83%	75% to 89%
Jun	149	150	99%	96% to 100%
Jul	74	80	93%	85% to 97%
Aug	61	63	97%	89% to 99%
Sep	43	48	90%	78% to 95%
Oct	73	76	96%	89% to 99%
Nov	22	22	100%	85% to 100%
Dec	0	3	too few examined

Peak flowering in Nov. Each bar is the share of Geranium robertianum in Vermont 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. 517 of 569 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 4 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 Vermont found Geranium robertianum in flower, not a forecast. It is computed only from observations made in Vermont, 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 Vermont. 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.