When does prickly sowthistle bloom in Vermont?

Most often in September. Across 56 dated, research-grade observations of Sonchus asper in Vermont, the flowering season runs roughly July to November.

Peak September In flower 56 Examined 62 State Vermont

Flowering 56 in flower of 62 examined

90%

85%

100%

86%

100%

Proportion of examined Sonchus asper in Vermont 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	0	too few examined
May	0	0	too few examined
Jun	0	0	too few examined
Jul	9	10	90%	60% to 98%
Aug	11	13	85%	58% to 96%
Sep	10	10	100%	72% to 100%
Oct	18	21	86%	65% to 95%
Nov	8	8	100%	68% to 100%
Dec	0	0	too few examined

Peak flowering in Sep. Each bar is the share of Sonchus asper 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. 56 of 62 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 Vermont found Sonchus asper 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

Sonchus asper

prickly sowthistle

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.