Japan's Obon (お盆) and Vietnam's Vu Lan báo hiếu look like two separate national holidays. They share a source: the Ullambana Sutra (盂蘭盆経), Ullambana being the Sanskrit term both names transliterate. The 盆 in Obon is the same character as the Bồn in Vu Lan Bồn.
Both begin with Maudgalyayana
The sutra tells of Maudgalyayana — Mokuren in Japanese, Mục Kiền Liên in Vietnamese — a disciple of the Buddha who used his powers to find his late mother and saw her suffering among the hungry ghosts. Asked how to free her, the Buddha told him to make offerings to the monastic community on the fifteenth day of the seventh lunar month. That instruction is the shared root of both festivals.
In Japan, records go back to the reign of Empress Suiko; it began as a court observance and spread outward. In Vietnam, Vu Lan is both a Buddhist occasion and an overlay on the folk belief that the seventh lunar month is the month for feeding wandering souls.
The dates differ because the calendars do
Obon most commonly falls on 13–16 August. But parts of Tokyo, Kanagawa and Shizuoka hold it on 13–16 July, and Okinawa and Amami still count by the lunar calendar, so their dates move each year.
The split dates from the calendar reform of 1873 (Meiji 6), when Japan adopted the Gregorian calendar. Some regions kept the number — the fifteenth of the seventh month — and read it as 15 July. Others shifted a month later to keep the season right. Both survived.
Vu Lan stayed on the fifteenth day of the seventh lunar month, because Vietnam still keeps festivals by the lunar calendar. On the Gregorian calendar it lands somewhere in August or September.
The rose on the shirt
Vu Lan has one custom Obon does not: at the temple, people pin a rose to their shirt. Red if their mother is living, white if she has died.
It is not an ancient practice. It spread from "Bông hồng cài áo", an essay the monk Thích Nhất Hạnh wrote in 1962. In little more than half a century it became the image most associated with the festival.
Where this matters at work
Japanese companies close for Obon. For a Vietnamese employee in Japan, the difficulty is that their own family observance falls about a month away from that break.
Asking for leave on Vu Lan means asking for leave during an ordinary working week. Explaining "the fifteenth of the seventh lunar month" rarely lands.
Knowing the two festivals share a sutra shortens the conversation considerably. One sentence does it: this is Obon, counted by the lunar calendar.