This seems like a simple question, but the if you ask five Bonsai artist what they use for Bonsai food, you'll get usually get seven different answers.
I've even had some Bonsai artist cringe for being asked such a question as if I were is asking an intimate question about their spouse. You'll find many Bonsai artist simply unwilling to share their secrets.
What I can do, is tell you what has worked for me in my 10 years of working with Bonsai trees.
Timing is important.
Late Spring and early summer is when Bonsai trees are most active and their feeder roots are actively searching for nutrients. This is one of the best times to fertilize your Bonsai.
I use a fertilizer called Island Supreme Nutricote 13-13-13, Controlled Release Fertilizer. If can't find 13-13-13, can can go as high as 16-16-16. You should be able to purchase at many home and garden stores.
You must use a fertilizer that is "Controlled Released". You may also see the word "Encapsulated" to describe the same type of fertilizer. What this means is there is a coating over the fertilizer that controls the release of nutrients.
Do not use fertilizer that is not "Controlled Released" or not "Encapsulated", it may kill your Bonsai if the nutrients are washed into to the soil too quickly by long periods of rain. (I learned that one the hard way.)
When fertilizing spread the fertilizer as far away from the trunk as possible, towards the outer edges of the pot. This encourages the feeder roots to reach out further to find nutrients and in time will produce a stronger, more extensive root system.
I usually fertilize at a couple of times a month, but sometimes forget or don't get around to it for longer periods.
Again, this is what has worked for me. There are many many different ways to fertilize a Bonsai tree, but this is what has worked for me.
Good luck with your Bonsai and let me know what works for you.
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