The grow cubes are about the size of croutons roughly 1/2 inch in size. They can be used for Moisture loving orchids like Phragmipediums, Cymbidiums, Cochlopetalum Paphiopedilums, Lycaste, Zygopetalums and Oncidinae. Having good water quality is important when using grow cubes. The fibers in the Grow Cubes are made from limestone which is heated and then spun into fibers and oriented in one direction, cut and cubed. Less fertilizer is needed so feeding every second or third time you water is ideal. These can be used straight out of the bag or amended with 15-20% large perlite for better aeration. Do not pack. Be sure to pre-wet these before use as the dust is very irritating. Wear Gloves. Can be reused. Fills 10 one gallon pots.