Lawn Fertilizer – Organic or Synthetic

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I am often asked which type of fertilizer you should use: organic or synthetic. Some gardeners have very strong opinions for using one or the other, but to make informed decisions, let us look at what organic and synthetic fertilizers are, and highlight the advantages and disadvantages.

What is fertilizer?

Humans and animals get nutrients through our diet. Plants must produce their own food from some essential elements, such as carbon, hydrogen, nitrogen, etc. Using the sun as energy source, the elements are turned into carbohydrates and proteins for leaf tissue, roots, genes, and DNA. This is a chemical process called photosynthesis.

The essential elements needed for plant growth are chemical elements. As example, Water is a product made up from two chemical elements: hydrogen (H) and oxygen (O). You may have heard it called H2O?? Fertilizers are also a collection of chemical elements, such as Nitrogen (N), Potassium (K), Magnesium (Mg), etc. Do you remember the “periodic table” from science class?

Fertilizers are products which contain collections of essential (chemical) elements needed for plant growth.

Grass plants primarily take up fertilizer elements through the roots. They do not care if the origin were organic or man made sources, as long as the nutrients are available in the chemical element form which they can use.

What is a synthetic fertilizer?

Synthetic simply means “man made” and the common nitrogen sources such as ammonia, ammonium sulfate, and urea are by-products from the oil and natural gas industry.

Synthetic fertilizers are typically manufacturered into salt compounds. You know what salt is?

Table salt (sodium chloride) is a collection of sodium molecules and chloride molecules held together (bonded). 

When placed in water, the water molecules will diverge on the sodium chloride, break the bonds between their molecules, and pull them apart into their individual chemical elements: “sodium” and “chloride” (strong little critters, aren’t they?). This is why salts tend to “melt” in water.

Plants need little sodium or chloride, and therefore table salt (sodium chloride) is not used as a plant fertilizer. Other salts may contain molecules such as potassium, nitrogen, calcium, and magnesium instead. These elements are useful for plant growth and are commonly referred to as essential (chemical) elements. Table salt is just one type of salt. There are many other types of salts, some of which “season the lawn”.

Because salt based fertilzers dissolve quickly into thier chemical elements, synthetic fertilizers are also referred to as “Chemical” fertilizers. Some people have then mistakenly assumed, that the fertilizers were similar to hazardous toxic waste. This is of course not true. While you certainly should not eat synthetic fertilizers, they are no more “chemical” than water and table salt. In fact, all fertilizers (synthetic or organic) are chemical (contain chemical elements).

What is an organic fertilizer?

Organic fertilizers are products which used to be “alive” (as plant or animals), or their waste products. Examples: horse manure and grass clippings are recycled and the essential (chemical) elements are released as fertilizer.

Typically, manures, dried blood, and fruit scraps are good sources of nitrogen and phosphorus. Plant tissues are made from cellulose but also contain fertilizer nutrients, such as nitrogen and magnesium, which will be released by the decomposing bacteria. Generally, green materials contain a lot more fertilizer whereas the brown materials have more cellulose and less fertilizer by volume.

The true biological definition of “organic” is compounds which contain the (chemical) element carbon (C). However, in gardening this definition is used differently.

Organic gardening is the growing of plants without the use of synthetic (man made) fertilizers, pesticides, and insecticides. One exception is mined fertilizer minerals. Natural deposits of rock phosphates, potash, and borate are allowed, even though these products were “never alive”.

NPK value of selected organic fertilizersOrganic fertilizers, unlike salts, will not dissolve in water directly. They consist of large, complex moleculess which must first be broken down by microbes. Organic nitrogen, for example, is available in proteins of animals and plants. It is converted from organic nitrogen into ammonium(NH4+) and then into nitrate(NO3-) by microbes. In one of these two forms, water can make the molecules available to the plants in the same manner as synthetic fertilizers.

Contrary to common belief, compost is not a good source of fertilizer for an actively growing lawn. Recycling grass clippings is a much better way to organically feed the lawn.

Justifications for choice of fertilizers

For the grass plants there is no distinction: a fertilizer molecule is a fertilizer molecule whether it was synthesized in a factory or was dumped from the back side of a horse.

Gardeners are the ones making the distinctions. Some prefer synthetic fertilizers while others prefer organics. These choices usually fall into 3 categories:

  • Plant oriented
    • Some plants benefit from organic fertilizers because timing and release speed matches growing conditions. Warm season grasses are one example. Other plants do better if fertilized with synthetic fertilizers. For example, late season fertilization of cool season grasses when soil temperatures are cool.
  • Cost, Availability, and Packaging
    • Synthetic fertilizers are usually concentrated, cheaper, and pre-packaged for easy transport, except when gardeners have access to free manure or compost. Because organic products generally contain lower percentages of nutrients, applications requires more work and volume. A 25 lbs bag of Lawn Fertilizer equals roughly 300 lbs alfalfa pellets
  • Personal beliefs
    • Some gardeners may not want to distribute manures and blood meal and are concerned with ecoli bacteria, mad cow disease, or offensive orders. Others may like organic products, because they prefer to recycle, to conserve nature, and to limit dependence of fossil fuels.

In most cases, gardeners are swayed by a combination of the 3 categories above. There are no right answers, but only preferences and choices.

Blurring the lines

It used to be a very simple definition: synthetic fertilizers were very concentrated products which worked well even in cold weather releasing their nutrients very quickly once dissolved in water. Organic fertilizers had to be supplied in large quantities, needed to be hauled in as bulk, were difficult to handle, but release speed matched growth of plants since nutrients became available gradually in warm soil.

Fortunately, it is not as straight forward as above because there are significant differences within each group of products.

Release Speed

Organic fertilizers generally release their nutrients slowly as microbes are required to break them down. However, organic products, such as dried blood and bone meal, release rather quickly, almost as fast as synthetic fertilizers.

Today, coated synthetic fertilizers are also available which mimics organics in their release time. There are even so-called IBDU coated synthetic fertilizers which release nutrients slowly even in cold soil.


It used to be easier to use synthetic fertilizers because they were pre-packaged and formulated with the optimum NPK ratio for lawns. Organic fertilizers have NPK ratios pre-determined from the source. For example, Milorganite (sewage sludge) 6-2-0 lacks sufficient potassium. This required organic gardeners to buy and mix several products.

However, today, products are readily available with optimal numbers, such as alfalfa horse feed pellets (2-1-2) and pre-formulated organic lawn fertilizers, such as Ringer Lawn Restorer 10-2-6 .

Synthetics can also come pre-packaged with weed and insecticide killers which can lead to in-optimal application times and overuse of pesticides.


While highly concentrated synthetic fertilizers are easier to transport, it is possible to apply very precise samll doses of nitrogen in late spring by using organic fertilizers which tend to have small NPK numbers, e.g. by using less product a gradual feeding can be control. This level of control is difficult to achieve with concentrated synthetic fertilizers.

Making the Choice

In my mind, it does not have to come down to a choice for or against. There is absolutely nothing wrong with mixing and matching based on the circumstances.

Unless you have already decided that organic lawn care is the only way forward for you, or you refuse to haul organics when turf builder is available, I always recommend looking at the growth pattern, the time of year, and the soil temperatures.

Next you review which type of fertilizer is best suited under the specific circumstances. Then you make your choice.

When it comes to lawns, I personally would use an organic product in spring on both cool and warm season lawns. This gives a gradual feeding early, just enough to keep cool season lawns green and growing through summer but without inducing a flush growth which can deplete storage reserves.

Warm season grass should not be fertilized too early in spring, and the slow release rate of organic fertilizers in cool soil matches the warm season root growth very nicely.

During hot summer months, using organic fertilizers provides some security for warm season gardeners as salt based fertilizers can burn lawns during the hottest months. Slow release coated fertilizers are preferred if synthetic sources are pursued. A cool season lawn should not be fertilized in summer with either synthetic or organic fertilizers.

In early fall, soil temperatures are typically warm enough to support either organic or synthetic fertilizers.

In late fall, warm season grass should not be fertilized. Cool season lawns benefit tremendously from a single application with a quick release fertilizer after the top growth stops, but while the grass is still green (November). Using an organic, or a slow release coated synthetic, fertilizer at this time will just leave the product suspended until next spring which defeats the purpose of the application. A soluble quick release synthetic fertilizer like ammonium nitrate or urea is here the best choice by far.

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