When does white snakeroot bloom in New Jersey?

Most often in December. Across 428 dated, research-grade observations of Ageratina altissima in New Jersey, the flowering season runs roughly August to December.

Peak December In flower 428 Examined 623 State New Jersey

Flowering 428 in flower of 623 examined

33%

76%

91%

82%

68%

92%

Proportion of examined Ageratina altissima in New Jersey in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	1	too few examined
Feb	0	0	too few examined
Mar	0	0	too few examined
Apr	0	14	0%	0% to 22%
May	0	42	0%	0% to 8%
Jun	0	33	0%	0% to 10%
Jul	9	27	33%	19% to 52%
Aug	38	50	76%	63% to 86%
Sep	155	170	91%	86% to 95%
Oct	163	198	82%	76% to 87%
Nov	52	76	68%	57% to 78%
Dec	11	12	92%	65% to 99%

Peak flowering in Dec. Each bar is the share of Ageratina altissima in New Jersey 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. 428 of 623 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 3 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 New Jersey found Ageratina altissima in flower, not a forecast. It is computed only from observations made in New Jersey, 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

Ageratina altissima

white snakeroot

Sourcesevery claim on this page

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