A more thorough explanation:

IN SOLO

in solo (in soh-loh), adv. & adj.
Latin In the soil or ground.

In solo is a Latin term that means "in the soil or ground." It is often used in scientific or agricultural contexts to refer to things that are found or grown in the ground.

• Many plants grow in solo, absorbing nutrients and water from the soil.
• Archaeologists often find artifacts buried in solo, preserved by the earth over time.
• Some animals, like moles, live in solo, digging tunnels and burrows underground.

These examples illustrate how the term in solo is used to describe things that are located or grown in the soil or ground. Plants, artifacts, and animals can all be found in solo, and the term is useful for describing their relationship to the earth.