From Nookipedia, the Animal Crossing wiki
Fertilizer NL Icon.png
A bag of Fertilizer placed on the ground

Fertilizer is an item in Animal Crossing: New Leaf that can be purchased at the Garden Shop section of T&T Emporium for 1,600 Bells.

The player can use a shovel to bury Fertilizer next to a flower to increase the chance of hybrids growing or next to a fruit tree to increase the chance of perfect fruit growing. The Fertilizer will take effect one day after it is planted. After buying 50 Fertilizer bags, Leif will give the player the Golden Shovel.

Beginning in the Welcome amiibo update, Fertilizer can also be used to revive dead perfect fruit trees.