Organic fertilizers are a popular way of growing natural vegetables and flowers without the use of synthetic fertilizers that are sometimes seen as detrimental to the environment. Some studies, including one by the United States National Institutes of Health, suggest that the manufacture of chemical fertilizers produces high levels of carbon dioxide. In addition, some high nitrogen fertilizers can add nitrous oxide to the atmosphere. Nitrous oxide and carbon dioxide are both greenhouse gasses.
Organic fertilizers have historically been the most common method of fertilization. Before the advent of petroleum-based synthetic fertilizers, organic fertilizers were the only types available. According to Iowa State University, organic fertilizers were the most common type of fertilizer before World War II.
The legal definition of a fertilizer is a substance that offers minimum percentages of nutrients intended to amend soil. Organic fertilizer is defined as a fertilizer that is derived from natural sources, such as plant and animal sources, rock powders, seaweeds and other sources that are either natural or biodegradable.
Types of organic fertilizers include compost that you can make at home by combing grass clippings and other vegetative wastes until they break down. Some animal manure, like cow, horse and chicken, can be composted. However, most dung composts are made and sold commercially. You can also buy plant-based composts from garden supply centers and some waste management companies. Meals, or powdered fertilizers made from various dried and ground products, can include fishmeal, kelp meal, blood meal, bone meal or seed meal. Each type of meal offers a different balance of nutrients. Some organic fertilizers are liquid. Examples include fish emulsion or kelp emulsion.
Organic nutrients release more slowly into the soil and have less of a tendency to burn roots. Because organic fertilizers release their nutrients more slowly, the risk of overfertilization and soil damage is lower. In addition, using organic fertilizer can help to improve soil health by introducing beneficial microbes and by helping sandy soils to retain water.
Some considerations when using organic fertilizers include the slow release of nutrients. In some cases, you may need nutrients to solve a sudden problem with a garden or crop. In those cases, judicious applications of synthetic fertilizers that can be taken up more quickly by your plants may be better. Another thing to consider is the type of organic fertilizer you use. Some organic fertilizers, like seed meals, are very high in nitrogen and can encourage leaf growth at the expense of flowers. For some flowering crops, you might want to use a more balanced organic fertilizer like fishmeal or fish emulsion as a fertilizer.