Greenery Day in Japan
Greenery Day in Japan is held on May 4. みどりの日 - Until 1988, April 29 was celebrated as the birthday of Emperor Showa. It was decided to keep this day a holiday even after his passing away in January 1989 and to name it Greenery Day because of the late Emperor's love of nature. In 2007, April 29 became Showa Day, and Greenery Day was moved to May 4. This event in the first decade of the month May is annual. 
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Officially, as its name suggests, it is a day to commune with nature and to be thankful for blessings. Today this day is celebrated as Greenery Day — Midori-no-Hi — with parades featuring elaborate floats, paper lanterns, traditional Japanese costumes, and fireworks. Popular places from which to observe the festivities in Tokyo include Tokyo Tower, the highest structure in the city, and Shiba Park. People also mark the day by planting trees and other activities centered around the appreciation of nature.
Similar holidays and events, festivals and interesting facts
Garbage Day in Japan on May 3 (Gomi No Hi);
Green Up Day in Vermont on May 4 (observed on the first Saturday of May, is a statewide effort in the US state of Vermont to clean up roadside trash);
National Air Quality Awareness Week in USA on May 6 (Starts on the first Monday in May);
World Cactus Day on May 10
International Argania Day on May 10
Switzerland’s Overshoot Day on May 13 (date for 2022);
All-Russian Forest Planting Day on May 14
Thai Buffalo Conservation Day on May 14 (Adopted 7 March 2017)