Types of Fertilizers & Their Best Uses

Updated May 19, 2022
Close up of male hand adding fertilizer to tomato plant

Whether you are growing plants in a home garden or operating a large-scale agricultural operation, the plants you are growing will need to be fertilized in order to thrive. The various types of fertilizers for plants can be divided into two broad categories: organic and non-organic (synthetic). Organic fertilizers are derived directly from plants or animals or are minerals used in their natural form. Inorganic fertilizers are manmade via manufacturing or chemical synthesis.

Organic Fertilizers

Organic fertilizers are used to enrich the soil with natural compounds that help plants grow and produce. They boost the level of organic matter that is present in the soil, while also promoting the reproduction of microorganisms that promote soil health. Examples of organic fertilizers include the substances listed below, though you should check the label to ensure that no inorganic materials have been added to them if your goal is to use truly natural fertilizer.

  • Animal manure - Composted animal manure (such as from cows, horses, or chickens) can improve soil texture and help it hold water better. It makes nitrogen available immediately and releases other nutrients over time.
  • Bone meal - Bone meal is a slow-release organic fertilizer that helps plants establish strong root systems by providing phosphorous and calcium. It can be used in powdered or spike form.
  • Fish emulsion -Fish emulsion is a liquid fertilizer used primarily to boost the nitrogen content in the soil. It also contains some phosphorous and potassium. It provides a quick boost and slow-release benefits.
  • Seaweed - Seaweed is a slow-release natural fertilizer that provides many key micronutrients and minerals, including copper, iodine, iron, manganese, potassium, phosphorous, and zinc. It can be used as mulch or brewed into tea form.
  • Worm castings - Worm castings are worm poop, a substance that improves soil structure, aeration, water retention, and nutrient retention. They improve seed germination and growth, as well as boost plant production.

Organic fertilizers are readily available from nurseries, garden centers, and agricultural suppliers. Organic fertilizers break down over time in the soil without leaving behind any kind of harmful residue. Rather, they leave the soil better than it was before they were applied.

Non-Organic (Synthetic) Fertilizers

Synthetic fertilizers are manufactured or made through a chemical synthesis process. These non-organic fertilizers provide crops with the potassium, phosphorous, and/or nitrogen they need to grow but do not enrich the soil over the long term. They are often used in commercial agriculture and in some home gardens, though care must be taken when storing or applying these substances. Inorganic fertilizers are sold under many brand names. Common inorganic fertilizers include:

  • Ammonium nitrate - Ammonium nitrate provides nitrogen to plants. It's produced via the reaction between gaseous ammonia and nitric acid. It is used as a granular fertilizer that may have added ammonium sulfate and anti-caking agents.
  • Iron sulfate - Iron sulfate, also known as ferrous sulfate, is obtained via the reaction of sulfuric acid on iron. It is used to acidify soil, so it helps plants that require acidic soil (such as blueberries and rhododendrons) get the nutrients they need.
  • Potassium chloride - Potassium chloride (KCL), often referred to as muriate of potash, provides potassium to agricultural crops. It is made by mixing potash (potassium hydroxide) with sodium chloride, then processing it into granular fertilizer.
  • Single superphosphate - Single superphosphate (SSP) is a phosphorous fertilizer produced via a reaction between phosphate rock and phosphoric acid. It provides a high level of phosphorous to crops, boosting strength and productivity.
  • Triple superphosphate - Triple superphosphate (TSP) is an even more potent phosphorous fertilizer than SSP. It's also available in granular and liquid forms. It provides the most phosphorous of any fertilizer that doesn't also contain nitrogen.

Sustained and/or excessive usage of inorganic fertilizers leads to a reduction in soil fertility over the long term. It impacts the soil's pH level and causes a reduction in microbial activity within it. Inorganic fertilizers can also be harmful to people and animals, as they contain ingredients that are harmful to both respiratory systems and skin. These fertilizers are highly water soluble, so they can leach into the bodies of water and groundwater, leading to widespread issues for plants, animals, and humans alike.

Choosing the Best Fertilizer

There isn't a one size fits all approach to choosing a fertilizer for your garden. It really depends on what you are trying to accomplish and the condition of the soil you are working with. It's really not an either-or decision. It's not ideal to rely solely on nonorganic fertilizers, but they also don't necessarily have to be completely avoided (though some gardners choose to do so). Generally, it's ideal to use a combination of both.

  • If you are looking for a quick solution to growing productive plants rather than enriching your soil over time, synthetic fertilizer can be a good option. However, as plants grow, they will use up the nutrients and the soil will be depleted.
  • If you are looking to build the quality of your soil, organic fertilizers are ideal becuase they do more than provide quick nutrients to plants. They work over time and help build soil health as they feed your plants. This is great, but it's not fast.
  • For new gardeners who have never worked on improving their soil, synthetics can help them get their garden going quickly, which is a good thing. In this case, starting with synthetic may be ideal, but then add organic throughout the season.
  • If your soil is already healthy, it's best to rely primarily on organic fertilizers, but there may be times that you face issues that would best be handled by using a synthetic fertilizer for a specific purpose (such as using iron sulfate to acidify basic soil).

Types of Fertilizer: Granular, Liquid, and Mulch Forms

Some fertilziers come in just one form while others are availalbe in multiple forms. You should focus first on choosing a fertilizer that provides the nutrients that your plants or soil needs, then selecting from the available forms for the particular type of fertilizer that you are purchasing.

  • Granular fertilizer can be sprinkled onto the soil or around the base of plants. It an also be worked into the soil. If it is water soluble, it can be mixed in water and sprayed on the plants.
  • Mulch type fertilizers are applied t the surface of the soil, covering empty areas and encircling the plants that growing in the area where mulch has been added. Their nutrients seep into the soil over time.
  • Liquid fertilizers come in a liquified form that should be diluted in water per package instructions, then sprayed onto the plants that you want to feed.

Understanding Different Types of Fertilizers

Both organic and non-organic (synthetic) fertilizer types are used in agriculture. Both types of fertilizer can boost plant yields by providing nutrients plants need to grow, but they have very different long-term impacts on the soil and its capacity to continue being fruitful. When looking at fertilizers in the store, be sure to carefully check the label of any fertilizer you are considering. It's important for you to be aware of what you are putting in your soil and how it may impact the soil, as well as any plants that are grown in it. Follow all recommended safety precautions and use fertilizer products only as directed.

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Types of Fertilizers & Their Best Uses