Roots Organics Big Worm Premium Castings Roots Organics Premium Worm Castings is a distinctive natural soil amendment. Our worms are carefully tended and fed an unparalleled blend of organic compost, rock dust and kelp for exceptional quality castings. In addition to containing Nitrogen, our castings also contain small amounts of Phosphorus and Potassium with naturally occurring micronutrients, minerals and beneficial bacteria. Worm castings contain Auxins and Cytokines, which are growth hormones that promote bigger and more fibrous plant roots. No fillers, no chemicals and no tricks. Just pure worm castings. 1 cu ft. size.