An emphasis on using organic products has been gathering steam for several decades due to the desire to be rid of pesticides, antibiotics, hormones, genetically modified organisms and other potentially harmful synthetic materials in the foods we consume.

But consumers are often more interested in ensuring their food does not contain the materials just listed than whether the fertilizer might or might not be synthetic. The term organic technically refers to something containing carbon, but for organic farming, it has a different definition. Generally, the understanding is that the end product is free from pesticides, toxins, antibiotics and hormones.

How Organic Fertilizers Work

Several organic compounds comprise the organic fraction of nitrogen in the soil. This nitrogen is released to root systems slowly, as microbes in the soil consume it and convert it to nitrates and ammonium, which are forms of nitrogen that are available for uptake by plants. Nitrates and ammonium build up in organic materials as a normal part of the soil decomposition process, beginning their cycle by feeding the soil bacteria.

By feeding the soil like this, organic nutrients produce a living soil teeming with beneficial microbes that help plants digest nutrients. This process usually takes 3-8 weeks or more, depending on various factors. So, feeding organic nutrients to your plants is a beneficial but slow process.

It is important to note that the term organic is not always synonymous with safe, and even if a fertilizer label states it is organic, you should still read it carefully. Some organic nutrients, such as cottonseed meal, can contain large amounts of pesticides, as cotton is difficult to grow without using pesticides to help control the insects that would otherwise eat the plants.

A Note on Nutrient Requirements

Plants need three macronutrients—nitrogen, phosphorus and potassium—and a number of micronutrients for general health and well-being. Fertilizers, both organic and inorganic, that contain all three macronutrients are considered complete nutrients, and those with equal percentages of all three are called balanced.

Plants also need a host of micronutrients, including iron, zinc, molybdenum, copper, chromium, manganese, cobalt, boron, selenium and sulfur. These are called trace nutrients because plants only need them in minute amounts, except for sulfur. Each of these micronutrients provides various benefits to plants, and a good understanding of the role each element plays is essential in determining what nutrients you need to provide your crop. Doing a little research in this area is vital to achieve high-yielding, quality crops.

Organic vs. Synthetic Nutrients in the Garden

Organic fertilizers increase both the physical and biological nutrient storage capacities of soils and decrease the risk of over-fertilization. Organic nutrient content, release and solubility are typically much lower than for synthetic nutrients. One study found that over a 140-day period, the organic nutrient had released 25-60% of its nitrogen content, while the synthetic fertilizer had released most of its nitrogen by the first leaching (around 20 days).

While the longevity of organic fertilizers is a major draw for gardeners, when you read the labels of many organic fertilizers, you may notice they often don’t contain all three macronutrients and often no micronutrients, either. There are several common ways an organic fertilizer will contain nutrients other than nitrogen. In the case of an animal-waste fertilizer, the animal might consume the specific nutrient in question.

For example, many bats feed on fruit, and fruit is high in phosphorus. Therefore, bat guano may be listed as containing a good amount of phosphorus. An organic fertilizer may also contain an added natural nutrient like rock phosphate to provide phosphorus. Naturally occurring minerals like this that are added to a fertilizer do not exclude it from being considered organic.

When it comes to synthetic fertilizers, inorganic minerals might be added, or the nutrients within the fertilizer may simply be processed to make them immediately available for plant uptake, while the nutrients themselves are actually extracted from an organic-based source.

Additionally, the fertilizer could be completely manufactured from a synthetic source, such as ammonium sulfate, which is manufactured by treating ammonia with sulfuric acid. Most synthetic nutrients are a form of salt. For example, iron sulfate and copper sulfate are forms of essential minerals that plants can uptake readily.

Combining Organic and Synthetic Nutrients in the Garden

There are many synthetic nutrients that can to be added to your primary organic fertilizer to make it more complete and provide the results you want. As mentioned already, some organic fertilizers lack the desired amount of various macro- or micronutrients for the crop being grown, or a particular phase of growth.

During the blooming cycle, for instance, most plants need more phosphorus than they needed during the vegetative phase. This is exactly where combining synthetic and organic nutrients can have a positive impact on the yields, health and flavors of your crops. For example, iron, zinc and sulfur play a major role in boosting the flavor of fruits and leafy vegetables.

Just because a fertilizer is synthesized does not mean it is dangerous to apply to plants grown for food, nor does it mean that consumption of the plant will be dangerous. What the fertilizer is derived from and combined with during the process of extracting or creating the final chemical or nutrient is an important consideration.

Too many synthetic nutrients and too little organic nutrients will rob the soil of the materials it needs to produce a large quantity of healthy bacteria and fungi. But because quality synthetic fertilizers used in the right amounts are not dangerous, you can safely add just the right amount of the various nutrients that crops need, in addition to the organic fertilizer you are using. This will create a living soil with plentiful microbial activity, while maintaining the correct supply of all nutrients needed, including nutrients the basic organic fertilizer may not have.

The right amount at the right time is important. Too much quick-release nitrogen early in a plant’s life will promote leafy growth instead of the root growth that is desired. Too little may result in yellowing leaves and poor growth. Similar troubles exist for other nutrients, only the symptoms are different. Because of the slow response of most organic-only regimens, it may be difficult to achieve the performance you want otherwise.

Using a small amount of synthetic fertilizer to boost and complement the organic can pay big dividends. As the soil matures, the number of beneficial micro-organisms increases, and the amount of synthetic nutrients can be reduced or even eliminated.

When soils are routinely changed out, however, in an attempt to minimize diseases or nutrient overload, the microbes in the soil may not have enough time to build to optimal levels. As with every other aspect of successful gardening, take notes, treat your crop like a science project and watch your yield and crop quality improve over time.