When does spreading dogbane bloom in California?

Most often in July. Across 271 dated, research-grade observations of Apocynum androsaemifolium in California, the flowering season runs roughly May to August.

Peak July In flower 271 Examined 302 State California

Flowering 271 in flower of 302 examined

82%

91%

98%

84%

64%

Proportion of examined Apocynum androsaemifolium in California 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	0	too few examined
Apr	0	0	too few examined
May	9	11	82%	52% to 95%
Jun	78	86	91%	83% to 95%
Jul	123	125	98%	94% to 100%
Aug	54	64	84%	74% to 91%
Sep	7	11	64%	35% to 85%
Oct	0	4	too few examined
Nov	0	1	too few examined
Dec	0	0	too few examined

Peak flowering in Jul. Each bar is the share of Apocynum androsaemifolium in California 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. 271 of 302 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 7 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 California found Apocynum androsaemifolium in flower, not a forecast. It is computed only from observations made in California, 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

Apocynum androsaemifolium

spreading dogbane

Sourcesevery claim on this page

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