Methods for characterizing living plants, wherein one or more beams of penetrating radiation such as x-rays are scanned across the plant under field conditions. Compton scatter is detected from the living plant and processed to derive characteristics of the living plant such as water content, root structure, branch structure, xylem size, fruit size, fruit shape, fruit aggregate volume, cluster size and shape, fruit maturity and an image of a part of the plant. Ground water content is measured using the same technique. Compton backscatter is used to guide a robotic gripper to grasp a portion of the plant such as for harvesting a fruit.