When does Sea Arrowgrass bloom in California?

Most often in April. Across 70 dated, research-grade observations of Triglochin maritima in California, the flowering season runs roughly March to April.

Peak April In flower 70 Examined 137 State California

Flowering 70 in flower of 137 examined

62%

73%

30%

55%

50%

33%

Proportion of examined Triglochin maritima in California in flower, by month
Month	In flower	Examined	Share	95% interval
Jan	0	0	too few examined
Feb	1	1	too few examined
Mar	13	21	62%	41% to 79%
Apr	16	22	73%	52% to 87%
May	7	23	30%	16% to 51%
Jun	12	22	55%	35% to 73%
Jul	11	20	55%	34% to 74%
Aug	7	14	50%	27% to 73%
Sep	3	9	33%	12% to 65%
Oct	0	2	too few examined
Nov	0	2	too few examined
Dec	0	1	too few examined

Peak flowering in Apr. Each bar is the share of Triglochin maritima 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. 70 of 137 examined observations were in flower, every one of them research grade. The whisker on each bar is a 95% Wilson interval. 5 months have fewer than 5 examined observations, so no proportion is drawn for them. 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 Triglochin maritima 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

Triglochin maritima

Sea Arrowgrass

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.