When does Zizotes milkweed bloom in Texas?

Most often in September. Across 1,133 dated, research-grade observations of Asclepias oenotheroides in Texas, the flowering season runs roughly April to September.

Peak September In flower 1,133 Examined 1,618 State Texas

Flowering 1,133 in flower of 1,618 examined

35%

68%

74%

79%

72%

73%

82%

55%

49%

Proportion of examined Asclepias oenotheroides in Texas in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	2	too few examined
Feb	4	4	too few examined
Mar	27	77	35%	25% to 46%
Apr	230	340	68%	63% to 72%
May	146	197	74%	68% to 80%
Jun	138	175	79%	72% to 84%
Jul	81	112	72%	63% to 80%
Aug	137	188	73%	66% to 79%
Sep	278	340	82%	77% to 86%
Oct	65	119	55%	46% to 63%
Nov	26	53	49%	36% to 62%
Dec	1	11	9%	2% to 38%

Peak flowering in Sep. Each bar is the share of Asclepias oenotheroides in Texas 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. 1,133 of 1,618 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 2 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 Texas found Asclepias oenotheroides in flower, not a forecast. It is computed only from observations made in Texas, 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 oenotheroides

Zizotes milkweed

Sourcesevery claim on this page

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