What Are The Various Types Of Fertilizers?
Although you can purchase it in boxes, bags, bottles, sacks, or in bulk, there are really only two types of fertilizers, organic and inorganic. Fertilizer collected in bulk form is more likely to be organic, while if it is comes in boxes or bottles it is most likely inorganic, though there are exceptions.
A Supplement, Not A Food - One can think of fertilizer as being the equivalent of supplements we take, such as a multiple-vitamin pill. We get most of our nourishment from the foods we eat, but some foods are deficient in certain minerals or other elements, so we often take supplements. Plants get their principle source of nourishment from sunlight, growing by the process of photosynthesis. Plants sometimes require additional nutrients from the soil, with different kinds of plants requiring different nutrients in differing quantities. We choose among the different types of fertilizers to ensure a given kind of plant gets the nourishment, the "multi-vitamin" it needs.
In general, organic fertilizers contain fewer nutrients by weight than do inorganic fertilizers. Inorganic fertilizers are chemical fertilizers and can be produced to meet specific needs. Organic fertilizers usually consist of animal waste such as cow manure, chicken manure, or bat guano, or compost consisting of decayed vegetation. Organic fertilizers tend to be better for the soil. They have to be worked into the soil where they release their nutrients somewhat slowly. It's difficult to achieve an over concentration of organic fertilizer. An over concentration of inorganic or chemical fertilizer on the other hand can burn plants, and in the long run be damaging to both the soil and to groundwater. Organically grown vegetables use strictly organic fertilizers, and are marketed as produce which has been grown without harming the environment in the process.
The types of fertilizers can be broken down further in to such categories as quick-release, slow-release, general purpose, and liquid. Most of these types tend to be inorganic, though a notable exception might be fish fertilizer, though inorganic supplements may have been added.
Vegetables And Flowers - There are general purpose fertilizers available that can be used for most plants, and are useful both in vegetable and flower gardens. In general however, if you are growing vegetables, a fertilizer higher in nitrogen, which promotes leaf growth would often be best, but might not be appropriate for the flower garden. Here you'd want less nitrogen and more potassium or phosphorous, to stimulate blooming. With too much nitrogen, flowers still may form, but plants may have an excess of foliage. Some plants, like tomatoes and roses do best when given a custom-made fertilizer. These plants will generally do all right if a general purpose fertilizer is used, but if you want larger, juicier tomatoes, or show-stopping rose blossoms, tomato fertilizer and rose fertilizer, respectively, would be the better choices.
The NPK Numbers - The numbers associated with different types of fertilizers, specifically inorganic fertilizers, refer to the three basic chemicals making up the fertilizer and the proportion of each chemical that will be found. The numbers refer, in order, to nitrogen (N), phosphorous (P) and potassium (K), and tell you not only the proportion of one element with respect to the other two, but how many pounds of that element (per 100 pounds of fertilizer) are in the box or bag. A 20-15-10 fertilizer would, per hundred pounds, contain 20 pounds of nitrogen, 15 pounds of phosphorus, and 10 pounds of potassium. A 5-5-5 fertilizer would contain five pounds of each, per hundred pounds. The remaining weight consists of fillers, compost, or other nutrients.
Don't be overwhelmed by the different types of fertilizers out there. Knowing a little about the plants you are growing, be they indoor, vegetable garden, flower garden, trees and shrubs, or lawn, will give you an idea of which types may suit you best. You can always fall back on a general purpose fertilizer or an organic fertilizer when in doubt.