When does Glacier Lily bloom in Idaho?

Most often in March. Across 154 dated, research-grade observations of Erythronium grandiflorum in Idaho, the flowering season runs roughly March to July.

Peak March In flower 154 Examined 161 State Idaho

Flowering 154 in flower of 161 examined

100%

97%

98%

91%

Proportion of examined Erythronium grandiflorum in Idaho in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	0	too few examined
Feb	0	0	too few examined
Mar	8	8	100%	68% to 100%
Apr	35	36	97%	86% to 100%
May	56	58	97%	88% to 99%
Jun	45	46	98%	89% to 100%
Jul	10	11	91%	62% to 98%
Aug	0	1	too few examined
Sep	0	0	too few examined
Oct	0	1	too few examined
Nov	0	0	too few examined
Dec	0	0	too few examined

Peak flowering in Mar. Each bar is the share of Erythronium grandiflorum in Idaho 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. 154 of 161 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 Idaho found Erythronium grandiflorum in flower, not a forecast. It is computed only from observations made in Idaho, 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

Erythronium grandiflorum

Glacier Lily

Sourcesevery claim on this page

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