Just like how we eat food for energy, plants need soil because the soil itself have nutrients that help plants survive, such as nitrogen and potassium that can only be found from the soil. If you dig out the soil and look at the bottom of trees and many plants, you can see a lot of roots. These roots help the plants and tree not only get necessary nutrients, but also retain wate that was dropped by rain or streams of water. Also, soil can help plants stay in one place and not get blown away.

Actually, plants don't always need soil. A lot of algae and seaweeds grow in water without soil. There's also a kind of farming or gardening called 'hydroponics,' where plants are grown in water with minerals and nutrients in it. You can read about it here:

Soil provides nutrients and minerals for plants. Soil keeps the plants in place, so they don't blow away in the wind. Soil keeps the water close to the roots, so the plants don't dry up in the sun. Maybe you can think of other uses for soil.

Plants' bodies are made up mainly of seven elements: hydrogen, carbon, nitrogen, oxygen, magnesium, phosphorous, and sulfur. Of these, carbon and oxygen the plant can get from the air, and hydrogen the plant can get from the water. The other four the plant cannot get from either the air or the water, and so needs to get it from the soil instead.

Note: the air is actually mostly nitrogen, but the chemical form that the nitrogen is in is a a form that plants cannot use. There are bacteria that can use that, and that's how nitrogen gets into the soil in the first place, but the plants still need the soil.

Plants, like any other organism need nutrients so that they can grow. While we take in nutrients through our mouths by eating food and water, plants don’t have mouths. What they do have, is they have roots that extend deep into the soil. The soil actually has a lot of nutrients in it because as organisms die and decompose, they become part of the dirt. From here, plants are able to absorb the good parts from the soil in the same way that we absorb the good parts from the food we eat. Essentially, plants use the soil as a medium to get food and water to their roots and then use that food to grow.

Soil is very important for plants. Soil holds the plants up and gives them structure. The roots of a plant grow downwards and hold on so that they can grow big and sturdy. Soil also supplies the plants with water and nutrients which help it grow, just like us!