When does tansy bloom in Massachusetts?

Most often in August. Across 213 dated, research-grade observations of Tanacetum vulgare in Massachusetts, the flowering season runs roughly August to September.

Peak August In flower 213 Examined 293 State Massachusetts

Flowering 213 in flower of 293 examined

30%

74%

98%

78%

69%

55%

Proportion of examined Tanacetum vulgare in Massachusetts 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	1	too few examined
Apr	0	11	0%	0% to 26%
May	0	13	0%	0% to 23%
Jun	3	10	30%	11% to 60%
Jul	58	78	74%	64% to 83%
Aug	88	90	98%	92% to 99%
Sep	36	46	78%	64% to 88%
Oct	20	29	69%	51% to 83%
Nov	6	11	55%	28% to 79%
Dec	2	4	too few examined

Peak flowering in Aug. Each bar is the share of Tanacetum vulgare in Massachusetts 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. 213 of 293 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 4 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 Massachusetts found Tanacetum vulgare in flower, not a forecast. It is computed only from observations made in Massachusetts, 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

Tanacetum vulgare

tansy

Sourcesevery claim on this page

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