Differences Between Fertilizers Derived from Organic and Synthetic Sources

By Jaime Staufenbeil - Milorganite Agronomist
July 3, 2017

The health of the soil—its ecosystem—is the most important factor to growing healthy lawns and plants. All fertilizers, whether derived from organic or synthetic sources, provide nutrients necessary for plants to grow. So, what’s the difference between organic vs. synthetic fertilizer?

Organic Vs Synthethic Fertilizer graphic

First, it’s important to understand the terminology. It’s confusing because the word “organic” is used in two very different ways and we tend to use it interchangeably, which is incorrect.

When it comes to fertilizer, “organic” refers to the source of the fertilizer’s nutrients. The nutrients in organic fertilizers are derived from natural plant or animal sources and their byproducts, which includes things such as worm castings (worm poop), horse manure, byproducts from wastewater treatment, as well as other natural materials. Not all fertilizers derived from organic sources can be used to grow produce that is “certified organic,” including biosolids, from which Milorganite is made.

“Organic certification” is strictly regulated by the United States Department of Agriculture (USDA) and recognizes four categories: crops; livestock; processed products; and, wild crops. Certification verifies that a “farm or handling facility complies with the USDA organic regulations.” Organic certification does NOT cover fertilizers of any kind, even those derived from organic sources.

  • Organic fertilizers are derived from natural sources.
  • Organic certification covers the process of how crops, livestock, and products are produced.

Synthetic fertilizers, sometimes called chemical or inorganic, are manufactured from mineral deposits, petroleum by-products, gasses from the air, and other materials.

Plants can’t tell the difference between the source of the nutrients since they’re processed by the plants in the same way, but that’s where similarities end. There are advantages and disadvantages to both types of fertilizer. Here’s a quick comparison to help you better understand the difference.

What are fertilizers derived from organic materials?

Fertilizers derived from organic sources are made from living things or their byproducts, including animal matter, manure, and vegetable matter, such as compost, cover crops, as well as microbes, which have digested organic matter in wastewater.

Here’s a list of some fertilizers derived from organic sources:

  • alfalfa
  • biosolids, such as Milorganite
  • blood and bone meal
  • compost
  • cottonseed and soybean meal
  • feathers
  • fish
  • kelp/seaweed
  • composted manure
  • mushroom compost
  • worm castings

Why use organic fertilizer derived from organic sources? The greatest advantage of organic fertilizers is their overall contribution to the soil’s ecosystem and support of long-term soil fertility. They are also far less likely to leach or run off into waterways. They often provide some of the 13 micronutrients plants need to grow and remain healthy. Organic fertilizers help feed the abundant microbes and other critters that maintain soil fertility. Results from using organic fertilizers may take longer to see but are effective longer.

What are fertilizers derived from synthetic sources?

Synthetic fertilizers are made from processed inorganic minerals and compounds, including petroleum, minerals, and gases from the air. They’re composed primarily of nitrogen, phosphorus, and potassium (N-P-K) and generally don’t include micronutrients or offer much at all to maintain the soil’s ecosystem. Synthetic fertilizers are good if you want to quickly see results.

Is Milorganite an organic or synthetic fertilizer?

Milorganite has some of the best qualities of both types of fertilizer. It’s a convenient, pelletized fertilizer derived from organic materials. The organic materials help keep the soil fertile and conditioned to retain water. Its nutrient analysis (N-P-K) is consistent and contains non-staining iron. It’s derived from dead microbes, so it won’t burn lawns or plants. It’s also cost-effective, easy to apply, and readily available in convenient, large bags for homeowners.

QualityOrganic (natural)Synthetic (chemical)
Purchasing Convenience
  • Depending on the type of organic fertilizer used, it can be more expensive than synthetic fertilizers.
  • Available bag sizes aren’t large or economical enough for homeowners.
  • Synthetic fertilizers are most commonly used, readily available, available in greater amounts, and generally, cost effective.
  • Controlled-release pellets are more expensive.
Ease of Application
  • Some organic fertilizers are in their “raw” form, not pellets, and may take extra effort to distribute over large areas.
  • Generally, no harm will result from over application or spills.
  • Use a fertilizer spreader according to manufacturer rates.
  • Accidental over application, including overlapping rows when fertilizing, can cause lawns to burn.
  • Natural-based fertilizer nutrients can fluctuate.
  • Micronutrients are typically present, providing some of the trace nutrients plants require.
  • Nutrient amounts are highly accurate.
  • Blends can be formulated for specific needs.
  • High nutrient concentrations may build-up in the soil, which may lead to leaching and run-off.
  • Generally, don’t contain necessary micronutrients.
  • If it contains water-soluble iron, it can stain concrete.
Rate of Nutrient Release
  • Nutrients are released at a rate plants can use, greatly reducing the chance of leaching or run-off.
  • Microbes in the soil break down the organic material releasing the nutrients.
  • Requires fewer applications, which means less work over time.
  • Controlled growth that doesn’t over-stimulate plants, promotes stronger root growth for better disease and insect resistance.
  • Reliant on soil temperature: cooler soil = slower release rate, which corresponds to the rate plants can take up nutrients.
  • Poor quality soils depleted of beneficial microbes may delay results.
  • Long lasting.
  • Synthetic fertilizers give lawns and gardens a quick, but short-lived, burst of nutrients, which can cause rapid growth at the expense of developing a strong root system.
  • May see results in 1–2 weeks.
  • More mowing will be required due to rapid growth.
  • Water soluble in most forms.
  • Because nutrients are released quickly more applications will be required.
  • Many forms available: pellets, granules, liquid, tablets, spikes, and controlled-release.
  • Short-term solution to a long-term need.
Impact on Soil
  • Promotes a healthy soil ecosystem.
  • Provides organic material that decomposes, releases nutrients plants can use and feeds vital microorganisms, all important for rich, fertile soil.
  • Improves soil texture, which increases water retention, particularly important in drought conditions.
  • Synthetic fertilizers contribute very little to the ecosystem or structure of the soil.
  • May actually decrease soil fertility due to chemical nitrogen stimulating excessive microorganism growth, which, over time, depletes organic matter in the soil.
Plant Safety
  • In most cases, won’t burn plant leaves or roots.
  • Manure should be composted for greatest safety.
  • Incorrect or over application may burn plants due to high concentrations of chemical nutrients, which are salts.
  • Can cause excess top growth and stress roots.
Environmental Safety
  • Minimal, if any, run-off or leaching.
  • Since water releases nutrients, a significant amount of nutrients can be lost from run-off and leaching, sometimes up to one-third.