Hello, I bought some slow release fertilizer from my local bonsai shop and they recommend 1 tbsp per gallon of the container. I have some 19" cubes for containers which come out to about 3.96 cubic feet per container. 3.96 cubic feet converts to about 29.6 gallons per container. Do I really need 29.6 tbsp of slow release fertilizer per container? That seems like a lot considering the actual root mass of the trees are probably half that. They are wide but not that deep, if that makes sense. The bottom of the containers have a few inches of large pine bark nuggets for drainage. I'd appreciate some advice. I don't want to burn my trees nor do I want to under fertilize which defeats the purpose. Thanks, Geoff
I use a 15-9-12 time release at roughly one-quarter to one-half teaspoon per gallon - roughly 1/12 to 1/6 of the rate you were advised. However, the roots are not going to populate the entire 19" depth of your containers. Only the top 6", or maybe 12" at most. In other words, the effective volume is only about 0.6 cubic foot or maybe only half of that (0.3 cuft). So, you only have something like 4 gallons to fertilize in each cube --> about 4 tablespoons at the rate you were advised (I would probably just do 2)
I knew it was way too high. They said 2-3 tbsp per bonsai container, so I’m a bit perplexed. They are 4 gallon containers. I guess they probably fill their containers more. I don’t know the specifics of the fertilizer. They just call it slow release. I’d rather be under than over. Thanks for the help.
