4″ x 4″ block for 1.5″ cubes to be transplanted into. Blocks are 4″ x 4″ x 2.5″ Terrafibre Slabs are a sustainable alternative to rockwool, peat moss, or coconut. Slabs are 100% biodegradable and compostable. The Slabs are highly absorptive. Hemp fibres can hold 1050% of its own weight in water, providing roots with the water they require.