When does Havana snakeroot bloom in Texas?

Most often in November. Across 241 dated, research-grade observations of Ageratina havanensis in Texas, the flowering season runs roughly January to December.

Peak November In flower 241 Examined 308 State Texas

Flowering 241 in flower of 308 examined

83%

70%

59%

80%

81%

89%

82%

Proportion of examined Ageratina havanensis in Texas in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	25	30	83%	66% to 93%
Feb	0	3	too few examined
Mar	0	4	too few examined
Apr	14	20	70%	48% to 85%
May	10	17	59%	36% to 78%
Jun	12	15	80%	55% to 93%
Jul	1	2	too few examined
Aug	0	1	too few examined
Sep	0	4	too few examined
Oct	61	75	81%	71% to 89%
Nov	78	88	89%	80% to 94%
Dec	40	49	82%	69% to 90%

Peak flowering in Nov. Each bar is the share of Ageratina havanensis in Texas 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. 241 of 308 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 5 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 Texas found Ageratina havanensis in flower, not a forecast. It is computed only from observations made in Texas, 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 havanensis

Havana snakeroot

Sourcesevery claim on this page

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