When does obedient plant bloom in Illinois?

Most often in August. Across 177 dated, research-grade observations of Physostegia virginiana in Illinois, the flowering season runs roughly July to October.

Peak August In flower 177 Examined 186 State Illinois

Flowering 177 in flower of 186 examined

93%

99%

94%

90%

Proportion of examined Physostegia virginiana in Illinois 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	0	too few examined
May	0	0	too few examined
Jun	0	1	too few examined
Jul	28	30	93%	79% to 98%
Aug	88	89	99%	94% to 100%
Sep	51	54	94%	85% to 98%
Oct	9	10	90%	60% to 98%
Nov	1	1	too few examined
Dec	0	0	too few examined

Peak flowering in Aug. Each bar is the share of Physostegia virginiana in Illinois 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. 177 of 186 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 8 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 Illinois found Physostegia virginiana in flower, not a forecast. It is computed only from observations made in Illinois, 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

Physostegia virginiana

obedient plant

Sourcesevery claim on this page

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