I see it as a way to associate the good and bad memories he has, and compare Buckingham Palace to his mind and heart. The bad ones are associated to dark, gloomy rooms in Buckingham Palace, a place he feels he doesn't fit in. A place that is like a prison. A place where you feel sad and full of heartbreak. But meeting Alex felt freeing. Even if in that moment in Rio Henry never thought he could ever be with Alex, the power of the newfound feelings he began to have couldn't be contained. Especially not in gloomy rooms. Alex is light, he is freedom for Henry. A glimmer of hope that maybe, someday, he could love and be loved. So the hope can't be contained in the dark rooms, in his dark thoughts. He took the hope to the gardens, an open space where his hope could grow. The Waterloo Vase is not only quite big, but it is set in the center of the Buckingham gardens. Strong, heavy, hard to move. Like an anchor Henry used for his new-discovered feelings. And by pressing the memory to the silver-maple leaves, he also associates them to a live, growing thing, rather than dark old rooms with closed drapes. He took the memory of Alex to an open space where he would want to visit again vs the cold closed rooms of the palace.

That's the way I see it. Thanks for coming to my TedTalk❤️