The best fertilizer you can get is natural composted vegetation with added manure, or equally good, redworm casings. But if you can't get these, then purchase slow release fertiizers. It has been found that fertilizers that release their nitrogen compounds and other nutrients slowly, allow the plants to grow more slowly, giving them time to absorb nutrients from the soil, and the fruits or veggies that grow on them to gather create the beneficial compounds, such as vitamins, minerals, and phyto compounds in greater concentration, than when quick release fertilizers are used. By using organic fertilizers such as manure and worm casings, you produce is healthier for you.
For a long time, I believed that fertilizer was fertilizer, except that most comercial varieties contain nitrogen rich salts that will over salinate soil over time, making it unusable in the long run.
It turns out that organic foods are healthier after all. Now, I just have to convince my eldest son about that. he sees no value in using organic products and believes that it just makes things more expensive.
Seeeeeeya; Goodweed of the North