When does Pacific rhododendron bloom in Oregon?

Most often in June. Across 485 dated, research-grade observations of Rhododendron macrophyllum in Oregon, the flowering season runs roughly May to June.

Peak June In flower 485 Examined 936 State Oregon

Flowering 485 in flower of 936 examined

33%

74%

84%

51%

15%

Proportion of examined Rhododendron macrophyllum in Oregon in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	13	0%	0% to 23%
Feb	0	25	0%	0% to 13%
Mar	1	32	3%	1% to 16%
Apr	14	42	33%	21% to 48%
May	144	195	74%	67% to 80%
Jun	230	274	84%	79% to 88%
Jul	89	176	51%	43% to 58%
Aug	2	64	3%	1% to 11%
Sep	1	40	3%	0% to 13%
Oct	0	30	0%	0% to 11%
Nov	4	26	15%	6% to 34%
Dec	0	19	0%	0% to 17%

Peak flowering in Jun. Each bar is the share of Rhododendron macrophyllum in Oregon 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. 485 of 936 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 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 Oregon found Rhododendron macrophyllum in flower, not a forecast. It is computed only from observations made in Oregon, 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

Rhododendron macrophyllum

Pacific rhododendron

Sourcesevery claim on this page

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