Plants must develop efficient root architectures to secure access to nutrients and water in soil. This is achieved during plant development through a series of expansion and branching mechanisms mostly in the proximity of root apical meristems, where the plant senses the environment and explores immediate regions of soil. We have developed a new approach to study the dynamics of root meristems in soil, using the relationship between the increase in root length density and the root meristem density. Initiated at the seed, the location of root meristems was shown to propagate, wave-like, through the soil, leaving behind a permanent network of roots for the plant to acquire water and nutrients. Mathematical models showed that the morphologies of the waves of meristems are inherent to individual root developmental processes, namely expansion, lateral root initiation and gravitropic responses. The "meristematic wave" observed in barley might be a more general and fundamental aspect of plant rooting strategies for securing heterogeneously distributed resources available in soil.