Green Dream is an excellent, well-balanced (6-6-6) slow release pellet fertilizer.
Most people underfeed their bonsai. This may be because they want them to stay small, so they don’t feed much, if at all. What you end up with if you don’t feed enough, may or may not be small, but it WILL be unhealthy.
Small is achieved primarily by pruning – both top and roots. True, you may not want to pump your bonsai up with artificially high concentrations of NPK and other nutrients, but you do want you bonsai to be at the peak of health, and regular application of balanced fertilizers are one of the keys to good health.
Dyna-Gro 7-9-5 is a well-balanced water soluble fertilizer that won’t burn roots, even when used at full strength.
Healthy trees take better to the deprivations of small container growing and other insults like severe top pruning, bending, carving and rootpruning, so make sure your bonsai get what they need, especially during the peak growing season from spring through mid-summer.
I like to fertilize using a combination of slow release organic pellets (Green Dream) in conjunction with a mild water soluble fertilizer (Dyna-gro). I also use fish-seaweed from time to time. All plants love fish-seaweed, which probably has the widest range of macro and micro nutrients of any fertilizer. The one downside is that it may attract unwanted four legged critters.
There is nothing as broad spectrum as fish-seaweed. Neptunes Harvest comes in 1 gallon size, 1 quart size, and an an 18oz size.