Is your houseplant thirsty? Are crops getting enough water? Is a forest at high risk of wildfire? Leaf health can answer all these questions, and researchers at The University of Texas at Austin have developed new technology to measure hydration levels with greater accuracy and without hurting the plant. The researchers developed an electronic tattoo for leaves that uses the hyperflexible and sustainable material graphene to track hydration levels. It sticks on the leaves without harming them, a major improvement over current methods that work only with dead or dried-out leaves or provide indirect measurements.