Premier PRO-MIX HP MYCORRHIZAE 3.8 Cu Ft.In Store Location: @Garage Trailers PRO MIX HP MYCORRHIZAE PRO MIX HP provides a superior growing environment for plants that require increased drainage and oxygen. Its Canadian sphagnum peat moss, perlite, dolomite and calcitic limestone fortified with beneficial endomycorrhizal fungus to strengthen roots and increase plants' ability to fully use available nutrients. 3. 8 cubic feet of compressed PRO MIX equals about seven cubic feet in use.