G-Blocks are the most cost effective method of tracking your water and subsurface moisture by electronic means. The blocks have been designed to provide a largest resistance range possible at the moist end of use where sensitive plants need monitoring. The large gypsum content of the block provides months of buffering soil solutions to assure that your really reading water content and not salinity or fertilizers. They are easy to install and simple to read and provide a reliable method for subsurface moisture monitoring. The Model 5201F1 Gypsum Blocks feature a slim, 7/8" (2.2 cm) diameter design and come in a variety of lead lengths. Once buried, depending on soil type and conditions, the blocks have a life span of 2-5 years. Available with 3, 6, 9, 15, 25 and 50 foot leads.