Organic fertilizers are more beneficial in the the long term for garden soils. As well as eventually releasing food for the plants, organic fertilizers help to improve the soil structure.
An organic fertilizer is basically derived from something that once lived. For instance ‘Blood, Fish and Bone’ is precisely what it says; but dried and crunched up. Farmyard manure should need no explanation! Some liquid fertilizers/feeds are derived from seaweed....
Generally speaking, they are slower acting than synthetic (man-made) fertilizers - no bad thing - and usually have a beneficial effect upon the soil, as well as feeding the plants. ‘Blood Fish & Bone’ is my favourite; the dried blood soon dissolves ready for the plant to feed upon.
The fish is the next to rot down, followed by the crushed bone. A veritable three course meal for the plants to feed upon! Bonemeal is one of the best fertilizers for long term growth in shrub borders and flower beds. Great for fruit crops as well.
For those who are not aware!! If for instance you use bonemeal - a great organic fertilizer - for feeding your plants. The plant does not actually feed on the bonemeal as such, but feeds on the chemicals that are eventually released in the decaying process of the bonemeal.
The bonemeal - after being worked upon by microbes in the soil - and therefore not too much good if used in potting soil or compost that does not have such microbes (!) releases phosphorus - a chemical, and calcium - a chemical. Bear in mind also that Bone meal was instrumental in the spread of Mad Cow disease - but when fed to livestock! This is simply to demonstrate that just because a product is classed as 'organic', it is not necessarily too different from 'Chemicals' which again need to be broken down in the soil by the said microbes.
There are those who swear by the use of organic fertilizers. It is interesting to note that most professional growers do not use them!