Fertilizers... No, I don't like to use them on landscape cacti. But, the containerized cactus will need some extra food now and then. I suggest once a month a light solution in the summer months only. Tomato food is fine to use as specialized cactus fertilizer is seldom available.   I use a fertilizer that has a high Phosphorous count(the number in the middle). Example 8-20-10:

• The 1st number (8) is Nitrogen which enriches the green coloring of the plant and promotes stem growth.
  
  
• The 2nd number (20) is Phosphorous which encourages flowering and root growth.
  
  
• The 3rd number (10) is potassium which strengthens stems and helps plants resist disease.
  
  

Good Luck and Happy Growing!