TL;DR: Cốc Vũ (穀雨) is the sixth of the 24 solar terms, usually beginning around 19 or 20 April and ending around 5 or 6 May, when the Sun reaches 30 degrees from the vernal equinox. The name joins cốc (grain) and vũ (rain), tied to the spring rains that feed the rice and bring all things to life, so in folk understanding it marks the shift from spring to summer, favourable for sowing. Old books such as the Tuế thời quảng ký record Cốc Vũ only through the words of calendar texts, with no rite of its own; in Vietnam this term is known mainly through the vạn niên calendar and farming experience, not as a festival with its own rites.
What is Cốc Vũ (Grain Rain) and when does it begin?
Cốc Vũ is the sixth solar term in the system of 24 solar terms. It begins around 19 or 20 April on the Gregorian calendar and ends around 5 or 6 May, when Lập Hạ (the start of summer) follows[1]. The name Cốc Vũ (穀雨) combines the character cốc (rice, grain) and vũ (rain); Vietnamese newspapers usually gloss it as "heavy shower"[1].
The Tuế thời quảng ký quotes the Tam thống lịch, which explains the name more literally: "穀雨為三月中氣" and "穀雨者言雨以生百穀", that is, Cốc Vũ is the middle qi of the third month, named so because the rain falls to bring forth the hundred grains[3].
In modern reckoning, which takes the spring equinox as the zero point where the Sun's longitude equals 0 degrees, Cốc Vũ corresponds to a solar longitude of 30 degrees[1]. In Vietnam time the term usually begins on 20 April, in some years on 19 April; between 1901 and 1975 there were 34 years in which it fell on 21 April. It lasts about 15 days and 10 hours, until the Sun reaches 45 degrees and Lập Hạ begins.
In the system of 24 solar terms, Cốc Vũ comes after Thanh Minh (Clear and Bright) and before Lập Hạ, and is the last term of spring. The Hiệp kỷ biện phương thư (欽定協紀辨方書, the Siku Quanshu edition) records three seasonal signs for this term, "萍始生，鳴鳩拂其羽，戴勝降於桑" (bình thủy sinh, minh cưu phất kỳ vũ, đái thắng giáng ư tang): duckweed begins to grow, the turtledove flaps its wings, and the hoopoe alights on the mulberry tree[2].
Why is Cốc Vũ important to farmers?
In folk experience, Cốc Vũ marks the transition from spring to summer, when the weather grows warmer, humidity rises and all living things flourish[1]. The term is tied to traditional farming, signalling a favourable season and a suitable time for sowing[1].
In the northern provinces, late April is the middle of the winter-spring rice crop, so rain at this time is watched closely by farmers. In the south, late April is still the end of the dry season, so the name of the term does not match the local weather as it does in the north.
What customs does Cốc Vũ have in old books?
Most customs attached to Cốc Vũ in old texts are Chinese customs, not Vietnamese ones.
According to the Siku Quanshu abstract, the Tuế thời quảng ký (歲時廣記) was compiled by Trần Nguyên Tịnh, a man of the Southern Song, in 4 juan; the book takes the Nguyệt lệnh, the Hiếu kinh vĩ and the Tam thống lịch as its framework, then draws on miscellaneous works that record matters related to the seasons, arranged by month: 46 entries for spring, 50 for summer, 32 for autumn and 38 for winter[3]. In its section on the last month of spring (季春月) in juan 1, the book mentions Cốc Vũ only through the words of the Hiếu kinh vĩ, the Tam thống lịch and the Chu thư Thời huấn: the direction of the Dipper's handle, the meaning of the name and the three pentads "穀雨之日萍始生後五日鳴鳩拂羽後五日戴勝降於桑", and records no rite of its own for this term[3].
Customs often mentioned around Cốc Vũ in China today, such as drinking Cốc Vũ tea or admiring peonies, do not appear in the Siku Quanshu edition of the Tuế thời quảng ký.
In Vietnam, Cốc Vũ is hardly a festival with its own rites. People know of Cốc Vũ mainly through the vạn niên calendar and through writing about the 24 solar terms.
Is there a difference between how Cốc Vũ is calculated in the old calendar and in the modern calendar?
The principle differs. The old calendar used the bình khí method, dividing the year into 24 equal parts of time. The Hiệp kỷ biện phương thư mentions this method when discussing the Hàn thực festival: "以古厯平氣計之清明在冬至後一百零六日半", that is, by the equal division of the old calendar, Thanh Minh falls 106 and a half days after Đông Chí[2]. The modern calendar uses the Sun's longitude, each term covering 15 degrees of the ecliptic; because the Earth moves at different speeds along its orbit, the terms are not equal in length.
In 2026, Cốc Vũ begins at 8:29 on 20 April, Vietnam time, and ends when Lập Hạ begins at 18:35 on 5 May. 20 April 2026 is the 4th day of the third lunar month; by the can chi cycle it is a Giáp Tí day, in the Nhâm Thìn month, in the Bính Ngọ year[1].
Start times of Cốc Vũ from 2025 to 2030, Vietnam time:
| Year | Start date | Time |
|---|---|---|
| 2025 | 20 April | 02:42 |
| 2026 | 20 April | 08:29 |
| 2027 | 20 April | 14:15 |
| 2028 | 19 April | 20:02 |
| 2029 | 20 April | 01:50 |
| 2030 | 20 April | 07:39 |
The table below summarises the main markers of Cốc Vũ according to modern reckoning:
| Item | Value |
|---|---|
| Order among the 24 terms | Sixth term |
| Previous term | Thanh Minh |
| Next term | Lập Hạ |
| Start date | Usually 20 April, in some years 19 April |
| End date | 5 or 6 May on the Gregorian calendar |
| Solar longitude | 30 degrees from the spring equinox |
| Length | About 15 days and 10 hours |
| Signs recorded in old texts | Duckweed grows, the turtledove flaps its wings, the hoopoe alights on the mulberry |
What do the different schools and old books say about Cốc Vũ?
The main difference lies in which of the 24 directions Cốc Vũ is assigned to, because there are two ways of arranging them.
The Hiệp kỷ biện phương thư places the 24 terms by the direction the handle of the Northern Dipper points to: "清明乙穀雨辰立夏巽", that is, Thanh Minh at Ất, Cốc Vũ at Thìn, Lập Hạ at Tốn[2]. The Tuế thời quảng ký quotes the Hiếu kinh vĩ to the same effect: "春分後十五日斗乙為清明後十五日斗辰為榖雨", fifteen days after Xuân Phân the Dipper's handle points to Ất, which is Thanh Minh, and fifteen days later it points to Thìn, which is Cốc Vũ[3].
The same Hiệp kỷ biện phương thư records the Sun's position: "穀雨日躔酉宮初度是為大梁之次", that is, at Cốc Vũ the Sun enters the first degree of the Dậu palace, in the Đại Lương station[2]. The book uses this position as the monthly general, which for the third month is at Dậu, and keeps the two apart: "月建視節氣斗杓也月將視中氣太陽也", the month branch follows the solar terms and the Dipper's handle, the monthly general follows the middle qi and the Sun[2].
Feng shui books on the compass use that solar position for the "thái dương đáo sơn" (Sun reaching the mountain) method: the table pairing the 24 mountains with the 24 terms reads "Thái dương cốc vũ đáo dậu sơn", meaning that at Cốc Vũ the Sun reaches the Dậu mountain. Practitioners use the table to choose days and directions; it is a convention of the discipline, different from placing Cốc Vũ at Thìn by the Dipper's handle.
Do the Vietnamese have any customs of their own at Cốc Vũ?
The short answer: there is hardly any custom bearing the name Cốc Vũ in Vietnamese culture. In 2026 the Hàn thực festival (the 3rd day of the 3rd lunar month) fell on 19 April, the day before Cốc Vũ began; families make bánh trôi and bánh chay to offer to the Buddha and to the ancestors[1]. In Vietnam, Hàn thực follows a fixed lunar date, not the solar terms, so it is a separate festival rather than a custom of Cốc Vũ.
Nhật Nguyệt's suggestions: how to make sensible use of Cốc Vũ?
Nhật Nguyệt's suggestion: if you choose days by the old books, remember that Cốc Vũ is a middle qi and does not change the month. The Hiệp kỷ biện phương thư counts the whole stretch from Thanh Minh to the end of Cốc Vũ as the month of Thìn ("從建辰者始清明終穀雨")[2]; the solar month only turns to Tỵ when Lập Hạ begins.
Nhật Nguyệt's suggestion: for farmers and gardeners, Cốc Vũ is a reminder that the rainy season is coming; irrigation and sowing should still follow each year's weather forecast.
