When does Threeleaf Foamflower bloom in Washington?

Most often in July. Across 1,670 dated, research-grade observations of Tiarella trifoliata in Washington, the flowering season runs roughly May to August.

Peak July In flower 1,670 Examined 2,134 State Washington

Flowering 1,670 in flower of 2,134 examined

17%

81%

91%

93%

80%

64%

66%

39%

28%

Proportion of examined Tiarella trifoliata in Washington in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	4	23	17%	7% to 37%
Feb	0	23	0%	0% to 14%
Mar	0	33	0%	0% to 10%
Apr	3	65	5%	2% to 13%
May	269	334	81%	76% to 84%
Jun	454	498	91%	88% to 93%
Jul	513	550	93%	91% to 95%
Aug	284	355	80%	76% to 84%
Sep	77	121	64%	55% to 72%
Oct	44	67	66%	54% to 76%
Nov	14	36	39%	25% to 55%
Dec	8	29	28%	15% to 46%

Peak flowering in Jul. Each bar is the share of Tiarella trifoliata 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. 1,670 of 2,134 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 Tiarella trifoliata 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

Tiarella trifoliata

Threeleaf Foamflower

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.