Essentially organic matter . Absorbs nitrogen as it composts or rots . When it is compost it releases nitrogen . Other things are at play but this is the main one . This is why a farmer has a manure pile . It needs to age . And compost . Same with plant matter . When it is composted . It is a great plant growing additive . The plants absorb the nitrogen . So for bonsai compost we want particles of a nice size to aid drainage . So you want something composted that still has . Size and texture . Bark and wood work well here . As there still is time for them to break down . Do not underestimate Mother Nature . Here . A forest floor is covered in leaves bark and rotted wood . The next layer is composted version of the top . Rich black high in nutrient soil . Drainage plays a key factor . The Japanese bonsai practitioners were smart . The part of the equation sone don’t understand . Is water wants to remain connected together . Even rain drops collect together . So gravity pulls the rain down it tries to stay together . Pulling oxygen into the soil as it drains . In a pot we break that bond . So we need all the drainage we can get . Also why a shallow pot has poorer drainage than a deep pot . So you want organic. Material rotted . That still retains shape and size . There for it absorbs and released fert . Naturally from itself or what you add . The modern fertilizers can . Relieve you if this . And some move completely to inorganic . Compost . Akso think hydroponics . But trees love organic matter . The trouble is getting something that lasts . And learning watering .
