Landscape plants and vegetable garden plants need nutrients to produce healthy vegetation. Those nutrients, like the macronutrients nitrogen, phosphorus and potassium, are pulled from the soil. If the soil lacks the proper nutrients for healthy plant growth, the plants will be less robust, producing fewer or smaller flowers or fruit. Nutrients can be added to the soil with plant fertilizers that will be either organic or inorganic and can come from different sources.
Plant sources for fertilizer are commonly referred to as compost and are organic. Compost is decayed vegetation that can come from landscape debris, such as clippings from healthy plants, or kitchen scraps, like ground-up banana peels, that have been allowed to decay, sometimes for up to a year. Leaf mold is another type of plant fertilizer where collected autumn leaves are kept in a cage-like structure that is exposed to rain and sun, prompting a natural decay process. Wood ashes are high in potassium or potash that can benefit azalea and other acid-loving plants to help raise the soil pH level.
Fertilizers may be made from animal byproducts, such as cow or horse manure (for phosphorus) or dried blood (for nitrogen), that are a result of processing animals, like cows, for consumption. Animal byproducts are organic when used as fertilizer. Farmers may have manure available for free to a gardener who only has to shovel and transport the product, or you can buy packaged manure. Manure has the added advantage of better water infiltration, shortening watering time.
Chemically created fertilizers (inorganic) are designed to meet specific plant requirements. The label on chemical fertilizer will contain three sets of numbers, such as 8-16-16, identifying the percent of the macronutrients nitrogen, phosphorus and potassium (or potash) contained in the product. The label will also identify plants or plant types that would benefit from the chemical compound. Leafy vegetables may call for a 12-12-12 blend, and azalea or rhododendrons may require a blend of 10-8-6.
Chemical fertilizers may be granular, powder or liquid. The latter two are most likely mixed with water for dispersing and are referred to as water-soluble fertilizers. The fertilizer may be "slow release" or "quick release." Slow release means the chemical is slowly absorbed by the soil and subsequently the plant, extending the benefit of the fertilizer. Most fertilizers are quick release, meaning the nutrients are rapidly sent through soil and do not last long.