Once again there are many different types of feed/fertilizer for bonsai use, and many discussions held on this subject.
As a general rule it is better to err on the side of caution, less is better than more.
Feed only during the growing season and not when trees are in their months of dormancy.
Feeds containing trace elements are also recommended.
I use mostly Maxicrop, a seaweed extract during the growing season and late Autumn Tomorite, a tomato feed.
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