You can make a rooting medium by mixing common materials such as sharp sand, grit or fine gravel, old weathered sawdust and coconut palm husks.Grit and fine gravel are good for aeration and drainage and they are clean whereas old weathered sawdust is good for moisture retention and has positive mechanical properties.Remember that most tropical sawdust has to be weathered by leaving it in the open for about a year to break down toxic chemicals.