Grodan 1" Starter / Cutting Seed Cubes - The SBS (single block system) is the most popular propagation block on the hobby market. The rockwool cubes are 1" in size. They are ideal for starting seedlings/cuttings, they can then be transferred into 7.5cm (three inch) cubes. Afterwards, the growing cubes are either planted onto rockwool slabs or into your hydroponic system or other substrate. Optimum strength and flexibility Free from root disease Ideal air to water balance Simple controllability of water and nutrients Strong root growth throughout the entire block. 150 cubes per tray