A method of determining health of a plant which method includes displaying, on a screen of an electronic display of a mobile computing device, a digital leaf colour chart with colours ranging from yellow green to dark green; displaying on the screen next to the digital leaf colour chart a white area on which a leaf of the plant is to be placed; receiving input to the mobile computing device from a user about which colour of the digital leaf colour chart that best matches the leaf placed on the white area; and the mobile computing device determining the plant health based on the received input.