Fertilizer for your garden comes in a variety of shapes and forms. Basically, fertilizer is a soil amendment that helps plants become more productive. It may be divided into two large groups: organic and non-organic. Organic fertilizers derive from things that were once living (plant or animal), while non-organic fertilizers are generally composed of synthetic chemicals and minerals.
The function of fertilizer is to amend or enhance the soil so that plants will grow bigger, better and heartier while producing more fruit and vegetables. Fertilizer is added in phases to the garden. It is applied to the soil prior to planting. This helps the plant to become hearty and well-established with strong stems, leaves and roots. Fertilizer is later reapplied as a side dressing or by some other method, such as a compost tea application. Applied at later stages, fertilizer assists in fruit production and increases yield.
Organic fertilizers include compost, compost tea, kelp or seaweed, fish meal, worm castings, vermicompost, manure, composted manure, egg shells and coffee grounds.
Non-organic fertilizers are primarily made up of the macronutrients potassium, nitrogen, and phosphorous. The proprietary blend may contain smaller amounts of secondary macronutrients calcium, sulfur, magnesium, iron and others. Non-organic fertilizers are characterized by numbers defining how much of each primary macronutrient they contain. Thus, the standard 10-10-10 fertilizer has 10 percent of nitrogen (N), 10 percent of phosphate (P205) and 10 percent of potash (K20). This is the national grade used for all non-organic fertilizers, and the numbers are always given in this order from left to right: N-P205-K20, or just N-P-K.
Benefits of Organic Fertilizers
In addition to increasing yield, organic fertilizers help improve biodiversity and long-term fertility of soil. Organic fertilizers are typically slow-release, which means the nutrients are released slowly over time instead of all at once. Organic fertilizers feed the plant directly and do not cause nitrogen burn as do many synthetic fertilizers. Organic fertilizers decompose naturally and can enrich the soil with living microorganisms. Organic fertilizer is not associated with nitrate contamination of groundwater, rivers and oceans as is synthetic fertilizer. Living plants can be used as organic fertilizer, as for example, cover crops. These can enrich the soil with both nitrogen and phosphorous without need for synthetic fertilizers.
Applying fertilizer can be a daunting task if you are new to gardening. However, there are some general guidelines that make the task easier. In the "old days" of gardening, a rural gardener might till up the soil into long rows, and then "broadcast" (or throw) the 10-10-10 standard fertilizer onto the soil. This would then be cultivated into the soil. After the garden was planted, the gardener would wait until growth emerged and then apply a side dressing of 10-10-10.
Organic gardeners might thoroughly mix compost, worm castings or manure into the soil and then plant, following with later applications of compost tea or side dressings of kelp or manure.
A soil analysis kit was once a thing only used by high-tech farmers and laboratory scientists. Today, you can buy them at the nursery or lawn and garden center. Using the soil analysis kit will show you, in detail, exactly what nutrients your soil lacks. You may then very precisely amend the soil with a fertilizer that contains those nutrients in the right amounts.
Nitrogen-rich synthetic fertilizers are known to contaminate ground water, eventually flowing to creeks, rivers and oceans. "Dead zones" in the ocean are attributed to fertilizer run-off, as well as excessive algae bloom, fish kills and "red tide." Nitrate contamination of ground water is harmful to humans at a level of 10 mg/L.
Persistent organic pollutants (or POPs) have been found to contaminate agricultural fertilizers and soil amendments.
There is a risk with using manure and composted manure as well. Remember that manure came from an animal and will necessarily contain whatever was inside the animal. This might have included unsavory things such as antibiotics, growth hormones, genetically engineered feed and various medicines. Buying manure from a local organic farmer mitigates this worry.