The three numbers on a fertilizer bag stands for N-P-K  Nitrogen-Phosphorus-Potassium.

Use a high phosphorus fertilizer for potted nectar plants.  This causes them to grow more blooms.  (Phosphorus is the middle of the three numbers on a fertilizer bag.  You can use a blossom-buster or other fruit-producing fertilizer.)  Use a high nitrogen fertilizer for potted host plants. 

Nitrogen causes the plants to grow more leaves.  Nitrogen is the first of the three numbers on a fertilizer bag.

Below: This bag is a balanced fertilizer – all three numbers are the same. 

Below: This fertilizer contains only nitrogen of the three (N-P-K).

Below: This fertilizer has more phosphorus, encourages flower/fruit growth and also encourages root growth. 

Potassium is good for overall health of the plant.

(Side note: male butterflies are attracted to fertilizer for its salt content)