When does Pipestem Clematis bloom in California?

Most often in April. Across 573 dated, research-grade observations of Clematis lasiantha in California, the flowering season runs roughly March to April.

Peak April In flower 573 Examined 1,111 State California

Flowering 573 in flower of 1,111 examined

56%

77%

79%

27%

Proportion of examined Clematis lasiantha in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	1	20	5%	1% to 24%
Feb	29	52	56%	42% to 68%
Mar	175	228	77%	71% to 82%
Apr	322	409	79%	75% to 82%
May	40	150	27%	20% to 34%
Jun	3	85	4%	1% to 10%
Jul	2	50	4%	1% to 13%
Aug	0	25	0%	0% to 13%
Sep	0	32	0%	0% to 11%
Oct	0	15	0%	0% to 20%
Nov	1	29	3%	1% to 17%
Dec	0	16	0%	0% to 19%

Peak flowering in Apr. Each bar is the share of Clematis lasiantha 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. 573 of 1,111 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 California found Clematis lasiantha 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

Clematis lasiantha

Pipestem Clematis

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.