National Mint Julep Day 
Were you desperately hoping for a refreshing bourbon cocktail but frustrated that you didn’t have a good enough excuse? Thankfully for you, Mint Julep Day is here to pander to your wildest fantasies… just as long as those fantasies involved sipping this classic cocktail.
https://www.daysoftheyear.com/days/mint-julep-day/
Water a Flower Day 
if it hadn’t been for coffee, cocoa, vanilla, lavender, camomile, marijuana, and many other flowering plants and trees, our world would have been a barren, dismal place. So Water a Flower Day is that yearly reminder to show our flowers how much we appreciate them for their sumptuous colours, their fragrant blossoms and their medicinal, or sometimes lethal, properties.
https://www.daysoftheyear.com/days/water-a-flower-day/
Loomis Day 
commemorates Mahlom Loomis, who patented his wireless telegraphing inventions on May 30, 1872 (whilst working as a dentist in Washington DC).
He had actually claimed to have succeeded in wireless telegraphy some 6 years earlier, though with no witnesses present to see this, May 30th is one of the earliest official recognitions of his triumph.
https://www.daysoftheyear.com/days/loomis-day/
Memorial Day 
is a federal holiday in the United States for remembering the people who died while serving in the country's armed forces.[1] The holiday, which is observed every year on the last Monday of May,[2] originated as Decoration Day after the American Civil War in 1868, when the Grand Army of the Republic, an organization of Union veterans founded in Decatur, Illinois, established it as a time for the nation to decorate the graves of the Union war dead with flowers.[3] By the 20th century, competing Union and Confederate holiday traditions, celebrated on different days, had merged, and Memorial Day eventually extended to honor all Americans who died while in the military service.[1] It typically marks the start of the summer vacation season, while Labor Day marks its end.
https://en.wikipedia.org/wiki/Memorial_Day
http://www.famousbirthdays.com/may30.html