When does box elder bloom in Vermont?

Most often in May. Across 112 dated, research-grade observations of Acer negundo in Vermont, the flowering season runs roughly April to May.

Peak May In flower 112 Examined 300 State Vermont

Flowering 112 in flower of 300 examined

78%

82%

Proportion of examined Acer negundo in Vermont in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	4	too few examined
Feb	0	9	0%	0% to 30%
Mar	0	5	0%	0% to 43%
Apr	65	83	78%	68% to 86%
May	47	57	82%	71% to 90%
Jun	0	14	0%	0% to 22%
Jul	0	17	0%	0% to 18%
Aug	0	22	0%	0% to 15%
Sep	0	21	0%	0% to 15%
Oct	0	25	0%	0% to 13%
Nov	0	26	0%	0% to 13%
Dec	0	17	0%	0% to 18%

Peak flowering in May. Each bar is the share of Acer negundo 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. 112 of 300 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. One month has fewer than 5 examined observations, so no proportion is drawn for it. 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 Acer negundo 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

Acer negundo

box elder

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.