When does American vetch bloom in Colorado?

Most often in April. Across 188 dated, research-grade observations of Vicia americana in Colorado, the flowering season runs roughly April to August.

Peak April In flower 188 Examined 200 State Colorado

Flowering 188 in flower of 200 examined

100%

92%

95%

87%

Proportion of examined Vicia americana in Colorado 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	0	too few examined
Apr	5	5	100%	57% to 100%
May	22	22	100%	85% to 100%
Jun	68	74	92%	83% to 96%
Jul	80	84	95%	88% to 98%
Aug	13	15	87%	62% to 96%
Sep	0	0	too few examined
Oct	0	0	too few examined
Nov	0	0	too few examined
Dec	0	0	too few examined

Peak flowering in Apr. Each bar is the share of Vicia americana in Colorado 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. 188 of 200 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 7 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 Colorado found Vicia americana in flower, not a forecast. It is computed only from observations made in Colorado, 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

Vicia americana

American vetch

Sourcesevery claim on this page

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