The hows and whys of bonsai fertilizer, fast and easy
The trick with bonsai fertilizing is to keep the tree healthy and vigorous without rampant growth. Let me assure you that there is no mystique to bonsai fertilizer. Yes, if you follow the traditionalists you’ll compound some concoction with cow bones, sheep blood, seaweed, and a bunch of other stuff. If you put that on your tree you’ll end up bugs, worms, and robins digging for the worms and bugs.
There is an easier way. You have a choice of chemical fertilizer or organic fertilizer. Chemical fertilizers are names like Peters, Ortho, Scott, Osmocote, and others. Chemical fertilizers are fast, easy, and inexpensive. I personally use a special one called Salé. I get it at Walmart at the end of the season. It’s under a sign that says "Salé 50% Off". I buy as many different brands as I can. I tend to avoid acid based brands.I get balanced blends, those listed as 10-10-10, or any other with the three numbers the same (or close). Once the tree is actively growing I tend to fertilize every two to three weeks at the manufacturer’s recommended strength. I rotate brands because each manufacturer uses a different blend of micro-nutrients. That way I get the full range over a few feedings. I stop about a month before dormancy. My last application is with a brand with a high phosphate component (the second number). That promotes healthy rootage going into dormancy. Even easier are the time release crystals such as Osmocote or Multicote. They are a once per season application, but, they are ugly laying on top of the soil. The trick here is to bury them under a top dressing of soil. Be sure to buy the version containing the greatest number of micro nutrients. The problems with chemical fertilizers are that they largely leach out after a few waterings and they leave salts behind. That requires occasional flushing with heavy waterings.
Ok, lets look at organic fertilizers. I wasn’t being facetious with blood meal, bone meal, and seaweed. There is an easier way. Most garden centers sell commercial organic fertilizers. The advantages of organics are that they are slow release, they support beneficial soil micro-organisms, and do not build up in the pot. The commercial organics are usually in meal or granular form. In addition to chemical fertilizers I use organics a couple of time a year. I’ll dig a hole in each corner of the pot, put a teaspoon full in each hole (more for large trees), and cover the hole. I might use Milorganite sprinkled on the surface since it’s black, small particle, and has extra iron (extra greening).
For junipers only -
While not a fertilizer you can use dolomitic lime to alter the color of junipers. Dolomitic lime will cause your tree to become a more intense green while acid based fertilizer, or agricultural sulphur, will cause a color shift to blue. Dolomitic lime is a brown granular product that blends in with soil quite well. Just sprinkle a spoonful over your soil. It's sold at most landscape nurseries.
Using this system takes very little time, effort, and money.
I've been doing bonsai since the late 70's. I'm passing on what I've learned in those 35+ years. These are real life techniques and tips that worked for me, but, may not for you. Remember, this is free advice and worth every cent of it.