When does Antelopehorn Milkweed bloom in Texas?

Most often in September. Across 1,867 dated, research-grade observations of Asclepias asperula in Texas, the flowering season runs roughly April to September.

Peak September In flower 1,867 Examined 2,719 State Texas

Flowering 1,867 in flower of 2,719 examined

35%

75%

73%

31%

48%

64%

81%

62%

Proportion of examined Asclepias asperula in Texas in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	0	too few examined
Feb	0	1	too few examined
Mar	56	160	35%	28% to 43%
Apr	1198	1600	75%	73% to 77%
May	464	635	73%	69% to 76%
Jun	47	154	31%	24% to 38%
Jul	15	31	48%	32% to 65%
Aug	7	11	64%	35% to 85%
Sep	38	47	81%	67% to 90%
Oct	41	66	62%	50% to 73%
Nov	1	12	8%	1% to 35%
Dec	0	2	too few examined

Peak flowering in Sep. Each bar is the share of Asclepias asperula 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. 1,867 of 2,719 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 3 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 asperula 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 asperula

Antelopehorn 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.