When does hyssopleaf thoroughwort bloom in North Carolina?

Most often in September. Across 107 dated, research-grade observations of Eupatorium hyssopifolium in North Carolina, the flowering season runs roughly September.

Peak September In flower 107 Examined 207 State North Carolina

Flowering 107 in flower of 207 examined

53%

96%

75%

17%

Proportion of examined Eupatorium hyssopifolium in North Carolina 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	0	1	too few examined
May	0	3	too few examined
Jun	0	15	0%	0% to 20%
Jul	2	43	5%	1% to 15%
Aug	27	51	53%	40% to 66%
Sep	50	52	96%	87% to 99%
Oct	27	36	75%	59% to 86%
Nov	1	6	17%	3% to 56%
Dec	0	0	too few examined

Peak flowering in Sep. Each bar is the share of Eupatorium hyssopifolium in North Carolina 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. 107 of 207 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 6 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 North Carolina found Eupatorium hyssopifolium in flower, not a forecast. It is computed only from observations made in North Carolina, 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

Eupatorium hyssopifolium

hyssopleaf thoroughwort

Sourcesevery claim on this page

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