When does common milkweed bloom in Rhode Island?

Most often in June. Across 133 dated, research-grade observations of Asclepias syriaca in Rhode Island, the flowering season runs roughly June to July.

Peak June In flower 133 Examined 429 State Rhode Island

Flowering 133 in flower of 429 examined

56%

55%

Proportion of examined Asclepias syriaca in Rhode Island in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	4	too few examined
Feb	0	8	0%	0% to 32%
Mar	0	1	too few examined
Apr	0	3	too few examined
May	0	34	0%	0% to 10%
Jun	58	104	56%	46% to 65%
Jul	74	134	55%	47% to 63%
Aug	1	53	2%	0% to 10%
Sep	0	37	0%	0% to 9%
Oct	0	36	0%	0% to 10%
Nov	0	12	0%	0% to 24%
Dec	0	3	too few examined

Peak flowering in Jun. Each bar is the share of Asclepias syriaca in Rhode Island 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. 133 of 429 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 Rhode Island found Asclepias syriaca in flower, not a forecast. It is computed only from observations made in Rhode Island, 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

Asclepias syriaca

common milkweed

Sourcesevery claim on this page

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