Significance Root growth in soil is complex. With limited sensory input, roots must navigate an environment containing heterogeneities such as rocks and compaction. The ability of roots to penetrate soil is crucial for water and nutrient uptake as well as mechanical anchorage. Here, we describe a molecular framework controlling helical root growth known as circumnutation. Functional characterization of circumnutation is consistent with the hypothesis that it is crucial for exploratory behavior and substrate penetration. This work lays a foundation for an integrated understanding of how roots grow in soil.