MEET IT IN 30 SECONDS
桜の開花・満開
Japan Meteorological Agency flowering dates record a defined stage on a designated sample tree. They help compare seasonal progress and climate, and appear in the news. A city’s opening announcement does not mean every cherry tree there has flowered.
The opening date is the first day the sample tree reaches at least five or six open flowers. The count concerns that tree rather than every cherry in a park, city or prefecture. Tokyo’s announcement can therefore differ from the condition of a particular viewing spot.
Full bloom is the first day about 80% or more of the sample tree’s flower buds have opened. JMA explains that checking every flower on a large tree is impractical and conditions change within a day. The threshold reflects a readily perceived state of full flowering. The interval after opening is not identical every year.
The observation guideline specifies that the flowers need not be open simultaneously; flowers that opened and have already fallen also count. The threshold describes flowering progress, rather than guaranteeing that eight in ten flowers remain on the tree that day or describing a particular viewing spot.
Somei-yoshino is the main subject because it is widespread and of public interest. Parts of Hokkaido use Ezo-yamazakura, while the southwestern islands use Hikan-zakura as a substitute. Regional comparisons require attention to species: early flowers in the south are not literally the same Somei-yoshino tree progressing north.
Muroran’s announcement of full bloom on 3 May 2025 identifies a Somei-yoshino sample tree at Muroran Hachimangū. It was six days earlier than the local normal of 9 May, but five days later than 28 April in 2024. Earlier than normal and later than last year are compatible comparisons.
Buds for the following spring form around summer and enter dormancy. Sufficient exposure to cold releases that dormancy; subsequent warmth supports development toward flowering. The sequence involves several seasons, rather than only the temperature immediately before the flowers open.
A mild winter can delay dormancy release by providing too little chilling, while later warmth can accelerate development. A 2024 Forestry and Forest Products Research Institute account of Somei-yoshino research examines these stages separately. Higher temperature cannot be treated as a guarantee of earlier bloom in every region and year.
Lines connecting places with similar opening dates describe the geographical progress commonly called the cherry blossom front. Flowers do not travel north in a moving band like a weather front. Latitude, altitude, local temperature and species produce differences within that broad pattern.
JMA standardized the subjects and methods of phenological observations and began the statistical series in 1953. Tokyo has earlier cherry records, but the standardized series has its own starting point. Its sample-tree observations moved to Yasukuni Shrine in 1966. Changes of site and tree provide context for long records.
Sample trees can age or become diseased. JMA’s guideline calls for checking species and variety and choosing a relatively open setting without excessive shade. A primary sample tree is normally accompanied by one or more backup trees.
Before replacement, flowering dates and other observations are compared with the primary tree for at least three years; the backup showing the smallest differences is selected, and the change is reported. If the primary suddenly cannot be observed, a backup meeting the comparison requirement can supply reports in the established order. This maintains continuity rather than averaging several trees or choosing whichever has the most flowers. Observers also check nearby plants of the same kind for an unusually large difference from the sample.
Forecasts use past flowering dates, temperature histories and expected weather to estimate a date yet to occur. Observation records a stage already reached. JMA ended its own cherry-opening forecasts after 2009 but continued opening and full-bloom observations. Private forecasts, official observations and a venue’s flower report describe different things. JMA’s 2009 discontinuation notice dates forecasts covering Japan except Okinawa and Amami to 1955. That forecasting history is distinct from the standardized observation series beginning in 1953.
A normal provides a comparison based on observations over a stated period, such as 1991–2020 in current materials. It is not a timetable each year must follow. Reading the date alongside its reference period and species helps separate annual variation from longer-term change. These observations also inform research on climate and plant seasonality.
No. It is based on a designated sample tree.
No. The threshold is about 80% or more.
Insufficient chilling can delay dormancy release.
No. It describes the geographical distribution of flowering dates.
Yes. Opening and full-bloom observations continue.
A replacement is selected after at least three years of comparison to minimize differences and maintain continuity.
No. Simultaneous opening is not required; flowers that have opened and fallen also count.