Fertilizers & Helping Your Plants Thrive

You can help your plants thrive by finding a consistent source, preferably free or at a very low cost. Once you see the difference fertilizing has on your plants you'll never look back. It serves as a little boost in the beginning of spring once it's warmed up a bit. You may or may not already notice fresh new growth emerging from your plants but then it would be the perfect time to add some fertilizer.
Fertilizers come from many sources and in different forms such as Powder, Granules, Compost or Liquid, etc. The main or let's say 'Macro' nutrients to look for are N for nitrogen, P for phosphorous and K for potassium. Think Up, Down & all around. N= Up/green growth, P= Down as in roots/establishment of the plant/flowering and K= All around/particularly aiding in flowering. We can get into micro nutrients later. They are far more numerous and detailed.
Make sure when you look at ingredients they sound like everyday items (Bat guano, Chicken/Cow/Steer manure, kelp, rice hulls). The synthetic type of fertilizer is not recommended because of the detrimental effect the runoff water with elevated fertilizer (Specifically Nitrogen) levels has on everything. A synthetic fertilizer bottle will read more like, 'Derived from: Ammoniacal nitrogen, Urea, Potassium Phosphate, Feric oxide', etc.
If you can avoid runoff water with fertilizer these 'synthetic' types can be used for ornamental & flowering plants.

Garden Soil vs Potting Soil

It's not dirt and it's never just soil. Choosing the right stuff for your use requires a little investigation as well as ignoring whatever pictures the manufacturers have put on the front of the package. First look for the words "Potting Soil/Mix" or "Gardening Soil", which make the biggest difference. You will notice that the potting soil is usually fluffier and more expensive in general (because of the added ingredients) versus the general gardening soils. That's because gardening soils are made with the intention that they will be mixed with established native soils. Specifically labeled potting soil has had ingredients (Perlite/Lava Rocks/Vermiculite, etc) added that allow for better water flow as well as overall air circulation to roots.
The second area you should read is the "Ingredients" or "Derived From" section. Here is where synthetic fertilizers will list ingredients such as Ammonium Phosphate, Ammoniacal Nitrogen, Urea, etc. On the other hand we have organic fertilizers, which will list Chicken manure, Bat Guano, Worm castings, compost, etc. This area can be crucial specially if you're looking to grow carrots, potatoes, onions or the like where your edible harvest will be in direct contact with those fertilizers in the soil. Otherwise many folks are generally quite comfortable growing and eating plants grown with synthetic fertilizers added to the soil.
In general you want to make sure that when you water your pot/soil picks up some of that water weight so you know its holding water, but the balance is that while watering it should freely flow through the soil and out the bottom of the pot. Otherwise too much water will be held leading to root rot and ultimate death of your plants. And there is no schedule anyone can give as to when or how much to water your plants. It all depends on what that species of plants generally prefers, how quickly it is growing, how many hours of direct sun it is getting, wind, room temperature, humidity and type of soil all play important roles, so the most important thing you can do is pay attention to your plants, give them a quick nudge to judge overall weight/water retention and look for signs of browning/drying on top soil to tell you if it MAY be time for more watering.