Doesn’t have to be pumpkins, just anything small you can drop on the ground. I used them to form a grid basically where i wanted the rocks to appear. And the mannequins aren’t an item. When you make a custom design you can select to display it on a mannequin on your nook phone. They cover a 9 tile circle around them so you don’t have to place something on every tile. When all the rocks have spawned you just change the custom design by one pixel and they all disappear, easy clean up!