Fertilizers can be categorized in one of two basic types: granular (dry) or liquid (wet). Technically, plants cannot tell the difference nor do they probably care. All fertilizers identify their ingredients according to the letters N-P-K in that order, always.
Not all fertilizers have Nitrogen (N) or Phosphorous (P) or Potassium (K). Whether they do or not is a decision made by the manufacturer. Regardless, the NPK sequence allows you to compare the different options, easily.
Granular or dry fertilizers can be mixed in the soil and released over time. They can also be top-dressed on top of the soil. One advantage is that their nutrients are released over time . One disadvantage is that you, the grower, has less control should the plants experience nutrient toxicity, due to someone (you) applying more of the product than recommended by the manufacturer.
Liquid or wet fertilizer is usually sold as a concentrate, but also diluted, ready to use by you.
There are two distinctions to consider. Base fertilizers are sold as either vegetative (grow) or blooming (flowers). The former promotes the leafy-growth of the plant, the latter the fruit and flower development.
The other type is called specialty fertilizer, designed not necessarily to provide the basic nutritional needs to the plant, but to promote root growth, for example.
Liquid fertilizers provide the grower (you) with more control and are easier to tailor based upon the plants' growth stage. Liquid fertilizers provide the plant with instant availability of their nutritional ingredients.
Plants cannot take up solids. The nutrients must first be made soluble. Whether you choose a granular or liquid version, both have to be mixed with water, made soluble, before you add it to your hydroponic system.
This is one of the primary reasons hydroponics provide plants with a faster growth rate and often a higher yield level. The plants do not have to wait for the fertilizer to be made soluble. They do not have to wait to be broken down. Plants do not have to search for their food. The plants' root systems are continually immersed in the solution . Their roots are in contact with their food at all times.
Grow a wide variety of salad greens in herbs in containers as small as one-half gallons.