First I thought it has to do with the measure "yard" but sitting in one yard is rather impossible unless you have the size of a dwarf and growing flowers or grass around would be very difficult.
I looked for an explanation and learned that when I sit in a yard in the States I sit in a piece of land next to a house, usually used for growing flowers, grass, and other plants. But that I do here in my garden. If I would have a yard it would be an area of land next to a building that is covered with concrete or other hard material. Not very cosy to say at least.
On the other hand you don't go to a gravegarden but to a graveyard maybe because there is more concrete than flowers ? You also don't turn around in circles in a prison garden but a prison yard, and you don't have a court garden but a court yard.
In short in the States I enjoy a yard and in Europe a garden. As long as I don't have to do garden work (or yard work ?) I don't care.
My American friends can be happy ! All our miseries started in a garden and not in a yard !!
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