Kiryu bonsai rock is used for special blend for special bonsai mixes. Kiryu is excellent for Pines & Junipers and Specimen Bonsai Tree - Slightly acidic mineral rich volcanic rock. - Hard particles, does not break down easy, will retain structure for several years. - Great for Pines & Junipers and old specimen bonsai trees. - Can be used on its own or mix with other growing medium and compost. - Japanese soil mixes usually include Akadama, Pumice, red lava rock makes a beautiful masters mix.