Fertilizer providing the N-P-K nutrients mentioned above can come in both organic and synthetic versions. What’s the difference?

Organic fertilizers come from sources such as manure, blood meal, cottonseed meal, feather meal, crab meal, etc. (Bear in mind: Not all products labeled “natural” are organic. Greensand—derived from inorganic mineral-based or “rock” matter—is an example of a natural, although inorganic, material.)

Organic fertilizers work in concert with soil microbes that break fertilizers down for plant uptake. Because they don’t add excess salts and acid to the soil, organic fertilizers are beneficial in encouraging healthy soil biology rich in microbial activity example is Super Gro Organic liquid Fertilizer and Natsoil Organic Fertilizer. While Super Gro is liquid, Natsoil is Soluble

Synthetic fertilizers are lab-made and derived from compounds like ammonium nitrate, ammonium phosphate, superphosphate, and potassium sulfate. They expedite plant growth and can contribute to bloom rate in flowering plants. However, they are high in salts and can be detrimental to populations of beneficial microorganisms and also leach into water sources. Applying too much synthetic fertilizer can “burn” foliage and damage your plants. Synthetic fertilizers are great for a boost, but do little to improve your soil’s long-term health, texture, or long-term fertility. Because synthetic fertilizers are highly water-soluble, they can also leach out into streams and ponds.
In general, organic fertilizers need time to enrich the soil, so they’re best applied in the fall so the nutrients will be available in the spring. For the spring, some fertilizers combine the best of both worlds with an organically-based fertilizer mix that also contains small amounts of synthetic fertilizers to ensure the immediate availability of nutrients.

Note that the N-P-K ratio of organic fertilizers is typically lower than that of a synthetic fertilizer. By law, the ratio label can only list nutrients that are immediately available.

GRANULAR VS. SOLUBLE FERTILIZERS
You may also notice that there are both granular and soluble formulations.

Granular fertilizers are solids that must be worked into the soil and given time (and water) before they dissolve and become available to plants. Examples are NPK Fertilizer and Urea Fertilizer
Slow-release fertilizers are a subset of granular formulations. A portion of the fertilizer is not immediately available to the plant. Nutrients are metered out over several weeks. Therefore, they are applied less frequently.
Sometimes called “liquid feed,” soluble fertilizers are sold as either ready-to-use solutions or packaged dry-milled materials that need to be dissolved in water. These tend to be quick-release fertilizers high in nitrogen that result in fast green growth. (Miracle-Gro is a good example of a soluble fertilizer.)
To build the long-term health and fertility of your soil, we recommend using granular organic fertilizers. Supplementing with an additional water-soluble fertilizer is a way to ensure that your plants have the nutrients they need when they need a boost (during active growth).

Soluble Fertilizers are like soil like fertilizer that can easily blend with the soil. Example are Natsoil Organic Fertilizer

SHOPPING FOR FERTILIZER
Shopping for fertilizer can be confusing because plants have individual nutrient requirements.

If you don’t have any specific soil needs, a 15-15-15 fertilizer is an all-purpose fertilizer that provides plants with what they need for healthy growth.
Evergreens — holly, rhododendron, yew, and others — not only need high nitrogen to keep them green, but several trace elements as well. Evergreen food may have an analysis of 30-10-10, plus a dose of copper, molybdenum, and iron.
Flowering annuals, on the other hand, burst into bloom when nitrogen is held back. The tonic they need is 5-10-10.
Good-quality bonemeal worked into the soil around newly planted bulbs keeps them springing up for several years.
ANOTHER KIND OF FERTILIZER: COMPOST TEA
Before buying bags or bottles of fertilizers, consider how you might add nutrients to the soil by improving its biology. Try compost tea, a liquid produced by extracting beneficial microbes (bacteria, fungi, protozoa, and nematodes) from compost.

Applying compost tea to both soil and plant foliage adds those beneficial microorganisms to the growing medium, which boosts plant health and encourages growth. Compost tea is made using a brewing process similar to that used for making beer. Active compost, a brewing kit, and a little information can go a long way toward turning your landscape into a thriving ecosystem. See information on how to make compost tea.