Soil is a surface type that can be found in a garden, which most plants can grow on. In Viva Piñata and Viva Piñata: Pocket Paradise, there is no soil in a garden at first, being made up entirely of hard soil, so the shovel is required to make soil suitable for plants. In Viva Piñata: Trouble in Paradise, a new garden starts out with a mix of grass and soil, along with other objects such as a fenced in Piñata as well as a flower surrounded by a path.
No Surface Packet exists for Soil, but any Surface Packet can be used to remove any other surface type other than water, such as Grass, Long Grass, Sand, or Snow. In Viva Piñata: Pocket Paradise the shovel can also be used to remove grass and long grass and turn it back to soil.
Whirlms are attracted to gardens with soil in it, meaning that most of the time Whirlms will gradually come into the garden.