Where dose soil come from? Soil is a blend of rock fragments watch air and humus that's carbon rich or organic materal left behind by living things. the humus makes the dirt more thiner and when it gets more thiner more animals can live there more often. What is in soil? Almost all plants need soil to grow. Soil must have important stuff in it. So plants must need minerals to grow. When things die they decompose and when they break down and turn into humus witch is thick and black. Plants get there food from the sun and the soil.