John Lennon and Yoko Ono had a big year in 1969. Following a quick wedding ceremony in Gibraltar, they hopped over to Amsterdam and used their honeymoon suite at the Hilton as a stage for their week-long “Bed-In for Peace” protest against the Vietnam War. A week later they were in Vienna wearing bags over their bodies and declaring the formation of a comical new philosophy called “bagism." Their goal, they said, was to promote "total communication" by getting people to focus on their message instead of their skin color, ethnicity, clothes, or in Lennon's case, hair length.

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These attention-grabbing antics were among their most famous peace efforts, but that same year they undertook a very different project. This time, away from the cameras, Lennon and Ono mailed acorns to some of the world's most important leaders and asked that they be planted in support of world peace.

The idea had been a year in the making. While filming a part for a movie called A Love Story on June 15, 1968, Lennon and Ono planted two acorns at England’s Coventry Cathedral, which had been bombed during WWII and was later rebuilt as a symbol of peace. They were “planted in east and westerly positions,” symbolizing the union of Lennon and Ono and their respective cultures.

Then, in 1969, they decided to scale up their "peace acorn" project. Along with two acorns placed in a small, round case, they sent world leaders a letter that read: “Enclosed in this package we are sending you two living sculptures—which are acorns—in the hope that you will plant them in your garden and grow two oak trees for world peace. Yours with love, John and Yoko Ono Lennon.”

Like the proverb “Great oaks from little acorns grow,” the couple understood the power of small gestures and wanted to start a conversation that would get world leaders thinking about the possibility of peace—or in Lennon's words, to encourage them to "give peace a chance."

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They did provoke some thought, at least. In a 1970 interview with Rolling Stone, Lennon explained, “We got reaction to sending acorns—different heads of state actually planted their acorns, lots of them wrote to us answering about the acorns. We sent acorns to practically everybody in the world.”

The two acorns were “submitted to Her Majesty [Queen Elizabeth II] in due course,” according to a letter that the Privy Purse Office at Buckingham Palace sent to the Lennons. A response from Malaysia confirmed that the acorns were to be planted in Kuala Lumpur’s Palace Gardens, and another letter from South Africa indicated that they would be planted on then-president Jim Fouché’s farm.

Golda Meir, then-prime minister of Israel, reportedly said something along the lines of, “I don’t know who they are but if it’s for peace, we’re for it,” Lennon told Rolling Stone. An official response sent by Meir’s assistant director in 1970 read, “Mrs. Meir very much appreciated the gesture, the underlying symbolism of which she would indeed like to see take root within a realistic framework.”

One particularly polite response came from Cambodia's head of state, Norodom Sihanouk, who worried he had erred in addressing Lennon and Ono as Mr. and Mrs. (he hadn't). He wrote, “Dear Sir and Madam, I may have wrongly assumed the friendly donators of acorns are husband and wife, and would like to submit ‘preventive’ apologies, together with my sincerest thanks for their gift.”

Norodom Sihanouk at a naval event in 1960Three Lions/Hulton Archive/Getty Images

Ono saved all of these letters, and photocopies can be viewed on her website. For his part, Lennon memorialized the event in The Beatles single "The Ballad of John and Yoko." In case you've ever wondered what the line "50 acorns tied in a sack" means, the verse in question references the events following their honeymoon and return to London:

Caught the early plane back to London
Fifty acorns tied in a sack
The men from the press
Said we wish you success
It's good to have the both of you back

To mark the 40th anniversary of the peace acorn offering in 2009, Ono recreated the act and sent acorns to 123 world leaders, including Barack and Michelle Obama. Next year, for the 50th anniversary, it remains to be seen if the famous peace acorns will again make their way around the world. If you happen to be a president or the Queen, you might want to save a spot in your garden, just in case.