My first devil fruit showed up in the fall of the 3rd year. It was extremely elongated and straight compared to the other fruits.
Using the devil fruit changes your tree depending on the season.
Spring - changes the colors of flowers
Summer - changes the species of tree
Fall - changes the shape and color of the container
Winter - changes the shape of the tree
Note: this is an early access solution. I've seen the first dragon fruit used in a season produce the expected change and using a second fruit in the same season do something random.