When does buck-horn cholla bloom in Arizona?

Most often in May. Across 342 dated, research-grade observations of Cylindropuntia acanthocarpa in Arizona, the flowering season runs roughly April to May.

Peak May In flower 342 Examined 643 State Arizona

Flowering 342 in flower of 643 examined

18%

38%

48%

67%

74%

13%

25%

29%

37%

35%

Proportion of examined Cylindropuntia acanthocarpa in Arizona in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	6	33	18%	9% to 34%
Feb	10	26	38%	22% to 57%
Mar	48	100	48%	38% to 58%
Apr	173	257	67%	61% to 73%
May	67	91	74%	64% to 82%
Jun	2	15	13%	4% to 38%
Jul	2	16	13%	4% to 36%
Aug	2	8	25%	7% to 59%
Sep	0	4	too few examined
Oct	5	17	29%	13% to 53%
Nov	10	27	37%	22% to 56%
Dec	17	49	35%	23% to 49%

Peak flowering in May. Each bar is the share of Cylindropuntia acanthocarpa in Arizona 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. 342 of 643 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. One month has fewer than 5 examined observations, so no proportion is drawn for it. 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 Arizona found Cylindropuntia acanthocarpa in flower, not a forecast. It is computed only from observations made in Arizona, 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

Cylindropuntia acanthocarpa

buck-horn cholla

Sourcesevery claim on this page

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