BACKGROUND: There is much interest in how roots can be manipulated to improve crop performance in a changing climate, yet root research is made difficult by the challenges of visualising the root system accurately, particularly when grown in natural environments such as soil. Scientists often resort to use of agar- or paper-based assays, which provide unnatural growing media, with the roots often exposed to light. Alternatives include rhizotrons or x-ray computed tomography, which require specialist and expensive pieces of equipment, not accessible to those in developing countries most affected by climate change. Another option is excavation of roots, however, this is time-consuming and near impossible to achieve without some degree of root damage. Therefore, new, affordable but reliable alternatives for root phenotyping are necessary. RESULTS: This study reports a novel, low cost, Rootrainer-based system for root phenotyping. Rootrainers were tilted at an angle, in a rhizotron-like set-up. This encouraged root growth on the bottom plane of the Rootrainers, and since Rootrainers open (in a book-like fashion), root growth can be easily observed. This new technique was successfully used to uncover significant genotypic variance in rooting traits for a selection of lettuce (L. sativa) varieties across multiple timepoints. CONCLUSION: This novel Rootrainertron method has many advantages over existing methods of phenotyping seedling roots. Rootrainers are cheap, and readily available from garden centres, unlike rhizotrons which are expensive and only available from specialist suppliers. Rootrainers allow the roots to grow in substrate medium, providing a significant advantage over agar and paper assays.This approach offers an affordable and relevant root phenotyping option and makes root phenotyping more accessible and applicable for researchers.