I'm looking for a Children's story I think was called Mr. Green Thumb. Where can I find it?

Mr. Green Thumb was an old man who always keep a real nice garden. he made friends with young kid who like to climb trees. After Mr. Green Thumb died, they young kid started to take care of his garden. The kid soon climbed a tree that Mr. green Thumb told him not to. In this tree was a letter from Green Thumb which included a Thanks for taking care of the garden. Have any one but me heard of this story? Where can I find it?