There are several forms of fertilizer for feeding Bonsai.

Liquid

Powder

Granules

Blocks or Cakes

Liquid fertilizer is quicker acting because it can soak through to the roots quicker and it can be absorbed through the leaves if it is used in a mister.

The Granules, Blocks or Cakes take 3 to 4 weeks to break down and each time the Bonsai is watered a little more feed washes through to the roots.

In general all fertilizer is made up of :-

Nitrogen (N)

Phosphorous (P)

Potassium or Potash (K)

shown on the pack by 3 numbers e.g.: 10-10-10

Nitrogen is good for leaf and stem growth .A Bonsai with pale leaves is a sign of too little Nitrogen.

Phosphorous is good for root development, thick and sturdy trunks and fruit ripening. A Bonsai with purple tinted leaves is a sign of too little Phosphorous.

Potassium is good for hardening young growth and protects against fungal attack. A Bonsai with a mottled colouring is a sign of too little Potassium

Soluble fertilizers can be used once a week during spring and early summer or use it at a quarter of the strength for every watering. Don’t make up soluble fertilizer stronger than the instructions on the pack as it could kill your tree.

The N P K balance will change with the time of year. In the spring a weak balanced ratio is required, say 5-5-5 or 6-6-6. Later when the shoots are extending it can be increased to 10-10-10 or 15-15-15. Late summer into autumn should be changed again to something like 0-10-10 for the dormant season. The exception to this is the Pine family which need low Nitrogen in spring and summer and higher Nitrogen in early autumn.

Tomato feeds can be used for flowering species and are typically 4-4.5-8.

Also sterilized bonemeal, typically 0-3.5-7.5. can be used if a flowering bonsai is producing lots of leaves but no blossom.
As you can see both types of feed have a similar amount of Phosphorous and Potash but the sterilized bonemeal doesn’t have Nitrogen in it so it will slow down leaf production.