Grodan's Delta Stonewool (Rockwool) grow blocks are made from molten basalt rock and chalk that are spun into fibers and then formed into blocks, cubes or slabs. It can hold up to 80-90% of its volume in water, yet leaving plenty of air space for root growth. Excess water will drain easily away. The MM 40/40 1.5x1.5x1.5" mini blocks are bundled 45 per pack.

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