For this achievement you first need to use your shovel to dig a bunch of seed holes. When you select the shovel you'll see an on screen prompt to dig a pong or to dig a hole, for this you need to dig a hole which you do by pressing the "A" button. Dig a bunch of holes relatively close together and then buy some candy from the store and place it well away from the holes, return to your garden and get the shovel out again. With the shovel out you need to hover over the candy and press the "X" button to putt it, doing this will send it across your garden and if aimed correctly it should end up in one of your seed holes.
I've linked in a video below where you'll be able to see an example of this.
* Credit to RoosterTeeth for the video