You don't need to fertilize new soil or new plants in new soil. If you do, you can cause problems with your plants. I have quite a few plants growing indoors and outdoors, and to be honest, I never have to fertilize. You would be surprised how long a plant can live in a container without a single feeding.
I use an EC meter and collect discharge water from the bottom of plants and test it. The need for fertilizer is almost "NEVER" need it, because I have over 300 ppm of nutrients in the containers. Most new soils run 1200 to 4900 ppm and adding any will most always cause problems.
Here's an example of a golden ivy Mother plant that's over 10 years old running on just rainwater now. Two months ago the ppm dropped below 200 and so I added liquid fertilizer. I used about 1/15th of the manufacturer's recommendation and the ivy is still looking good at over 300 ppm. If I would of added the recommendations I would of killed my plant.