The optimal provision of green roof services is largely dependent on the health of the vegetation on the green roof, which is often affected by water availability.We assessed the impact of two substrate components, brick particle size and a polyacrylamide gel additive, and a living mulch (companion planting of Sedum spp.) on the growth, physiological and visual health of newly established plugs of Festuca ovina and Linaria vulgaris during an extreme drought (25 days) in a controlled environment greenhouse. Polyacrylamide gel and large brick substrates increased both plant species' drought tolerance whilst a Sedum living mulch had no effect. Polyacrylamide gel increased the reservoir of water that plants could access during the drought, whilst large brick promoted slower and therefore more drought resistant plant growth. Overall this study shows that polyacrylamide gel and coarser particle size substrates can significantly improve the drought tolerance of green roof plants.