Organic or natural granular
Organic fertilizer comes from an organic source such as manure, blood meal, cottonseed meal, feather meal, crab meal, or others, as opposed to synthetic sources. There are also some natural fertilizers that are not organic, such as Greensand, which contains potassium, iron, calcium, and other nutrients. These are considered okay for organic gardening because they are not synthesized, but come from natural mineral-rich deposits in the earth. Organic fertilizers depend on the microbes in the soil to break them down into digestible bits for plants. Organic fertilizers tend to encourage soil microbes, earthworms, and other flora more than synthetic fertilizers do, because most organic fertilizers don’t add excess salts and acid to the soil. Microbes aren’t very active when the soil is colder than 50 degrees, and according the USDA, a rule of thumb is that for every 18-degree increase in soil temperature, the microbial activity doubles. Therefore, you have to be careful about applying too much organic fertilizer, because if microbial activity releases more nutrients than the plants take up and the soil can hold, the excess can wash away. Typically, a gardener might overload the soil in spring, when it is cold, but won’t know it until summer warms things up and the tomatoes are all leaf with no fruit!
Liquid fertilizers are water-soluble powders or liquid concentrates that mix with water to make a fertilizer solution. They can be messier than granular types because of the mixing, and some contain a blue or green dye that makes for easy identification but can stain. They usually require a hose-end sprayer or watering can. The liquid nutrients generally last 1 to 2 weeks, so you need to reapply often. The advantage of liquid fertilizers is that they are quickly absorbed, so plants get their benefits soon after you apply them. They are great as a starter solution and for a quick boost during the growing season. These fertilizers are also useful to supplement granular fertilizers for potted plants because frequent watering of containers leaches nutrients. Fish emulsion is a popular organic liquid concentrate fertilizer, but be forewarned that if raccoons and other critters are a problem in your garden, you my find some digging around fresh applications until the fishy aroma is gone