When does Scotch Broom bloom in Washington?

Most often in May. Across 506 dated, research-grade observations of Cytisus scoparius in Washington, the flowering season runs roughly April to June.

Peak May In flower 506 Examined 663 State Washington

Flowering 506 in flower of 663 examined

23%

59%

94%

99%

85%

34%

20%

21%

20%

75%

53%

Proportion of examined Cytisus scoparius in Washington in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	5	22	23%	10% to 43%
Feb	7	31	23%	11% to 40%
Mar	23	39	59%	43% to 73%
Apr	144	154	94%	88% to 96%
May	228	230	99%	97% to 100%
Jun	57	67	85%	75% to 92%
Jul	12	35	34%	21% to 51%
Aug	4	20	20%	8% to 42%
Sep	3	14	21%	8% to 48%
Oct	4	20	20%	8% to 42%
Nov	9	12	75%	47% to 91%
Dec	10	19	53%	32% to 73%

Peak flowering in May. Each bar is the share of Cytisus scoparius in Washington 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. 506 of 663 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 Washington found Cytisus scoparius in flower, not a forecast. It is computed only from observations made in Washington, 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

Cytisus scoparius

Scotch Broom

Sourcesevery claim on this page

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