Garden & Greenhouse


Organic Fertilizer Overview

Posted November 26th, 2013 by Eric Hopper in , ,

The Organic Kitchen Gardener

Our culture is becoming more aware of how our day-to-day routines impact our environment and our personal health. The greenhouse hobbyist is no different. There has been and will continue to be, a rise in environmentally conscious and organic products available to hobbyist gardeners. This is a direct reflection of the desires of the consumers who are beginning to understand how little changes can make a big difference.

Greenhouse hobbyists who want to optimize a plant’s growth will supplement nutrition to do so. In the past, both hobbyist and commercial growers have reached for conventional, chemical fertilizers to achieve their goals. In more recent years, advancements in organic fertilizers and supplements have allowed hobbyists and commercial growers to achieve similar results without compromising the health of the soil or themselves. Organic fertilizers can be broken down into two types: granular or liquid.

Granular Organic Fertilizers

Granular, or powder, organic fertilizers are commonly used to amend the soil with organic material which gives a desired nutritional value or other beneficial effect. Granular organic fertilizers include individual ingredients such as blood meal, bone meal and bat guano. Granular organic fertilizers can also be a combination of various individual ingredients sold for a specific purpose. Many organic fertilizer companies will create particular blends of individual ingredients and then market them as “rose blend” or “vegetable blend”. These blends are designed according to the nutritional needs of the plants. For example, a “vegetable blend” will most likely contain a mix of ingredients with enough nitrogen, phosphorus, and potassium to promote healthy growth and fruit development.

Granular organic fertilizers can be mixed into the soil prior to planting or used as a top-dress after the plants are established. Most granular organic fertilizers are not instantly available for nutrient uptake and some aren’t even soluble in their raw form. In other words, it takes some time for the organic material to break down into a form which can be used by the plants. This can cause problems for a procrastinating gardener. One way around this is to brew a tea from organic granular fertilizers. Tea brewing is a great way to extract the nutritional “goodies” from an organic granular fertilizer by turning them into a nutrient-rich liquid. Organic fertilizer tea brewing is usually done in a manner that is similar to the way one would steep tea (hence the name). Traditional tea is brewed with heat which would be counterproductive for organic fertilizer tea brewing as it would kill many of the beneficial microorganisms. Instead of heat, oxygen is used to multiply beneficial microorganisms and to stimulate the extraction process. This may sound pretty technical but in reality most organic tea brewing devices consist of nothing more than a five-gallon bucket and a small aquarium air pump. Brewing your own tea from organic granular fertilizers is a great way to gain an immediate benefit from fertilizers that would otherwise take some time to break down and become soluble. A note of caution: brewing teas from materials like bat guano or worm castings can be extremely stinky and messy. If this is something you would like to experiment with, make sure to have a dedicated area for your tea brewing (preferably with adequate ventilation).

Liquid Organic Fertilizers

Liquid organic fertilizers are the cat’s pajamas when it comes to optimizing organic nutrition for plants. This is because most of the nutrition contained within liquid fertilizers is ready for absorption by the plants. Many of the organic liquid fertilizers are essentially teas brewed and stabilized by the manufacturer. Organic liquid fertilizers are more expensive than making your own teas but are much more convenient (and less messy).

Gardeners and growers who wish to supplement their plants’ nutrition with liquid organic fertilizers should start by finding a “base” fertilizer. Think of the base fertilizer as the foundation of the plant’s diet. Base fertilizers generally contain a wide variety of ingredients with a balanced portion of both micro and macronutrients. Many times base fertilizers are divided into two categories: grow and bloom. “Grow” base fertilizers usually contain a higher ratio of nitrogen and are designed to promote vigorous vegetative growth. These fertilizers are generally supplemented throughout the early part of the growing season. “Bloom” base fertilizers usually contain a higher ratio of phosphorus and potassium and are designed to promote flower and fruit growth. These fertilizers are used later in the growing season after the plants show the first signs of fruiting or flowering.

Granular organic fertilizers and liquid organic fertilizers can both be broken down into two categories: direct nutrition additives and non-nutrition additives.

Direct Nutrition Additives

Fertilizers that contain some (or all) of the essential elements required for plant processes are considered direct nutrition additives. Both “grow” and “bloom” base fertilizers would fall under the category of direct nutrition additives. In fact, any product that has an N-P-K value displayed on the packaging is a type of direct nutrition additive. This holds true for granular fertilizers as well as liquid fertilizers even though the nutrition contained within the granular fertilizers will take some time to become available to the plants.

Non-Nutrition Additives

Fertilizers that do not contain essential elements for plant growth but help to deliver nutrition or offer some other benefit to plant functions are classified as non-nutrition additives. There have been some incredible advancements in organic direct nutrition additives over the years but it is the innovative non-nutrition additives that have really promoted the evolution of organic fertilizers. Scientists now understand the importance (and the complexity) of the symbiotic relationships between beneficial microorganisms and plants. This is why many of the non-nutrition additives are designed to supplement, stimulate, or otherwise enhance the microorganisms in and around the plants. By strengthening the symbiotic relationships between the microorganisms and the plants, horticulturists are able to maximize nutrient absorption organically. There are four non-nutrition additives that have revolutionized organic fertilization programs for both commercial and hobbyist growers. The four additives are: beneficial microorganisms supplements, carbohydrate supplements, enzyme supplements, and amino acid supplements.

Beneficial Microorganisms Additives

Some of the most revolutionary organic products to hit the horticultural market are beneficial microorganisms additives. Because of the importance of the symbiotic relationships between these microscopic creatures and the plants, horticulturists are able to accelerate plant functions by supplementing additional beneficial microorganisms to the soil or feeding program. These beneficial microorganisms serve two important functions: to aid in the break down and absorption of organic material and to feed on pathogenic organisms (therefore protecting the plant). Beneficial microorganisms additives can be found in both liquid and powder form and can be used to condition the soil or added to the soil throughout the plant’s life cycle. Supplementing beneficial microorganisms is a great way for greenhouse hobbyists to get the most out of their organic fertilizers and/or soils. Soils with high populations of beneficial microorganisms help to facilitate accelerated nutrient absorption which increases growth rates and fruit production.

Carbohydrate Additives

Carbohydrate additives, also known as soil sweeteners (not to be confused with sweetening a soil by use of dolomite lime), are designed to feed the microorganisms found in and around a plant’s root zone. Many beneficial microorganisms use sugars secreted by the plant’s roots as food. After feeding on sugars, they expel enzymes which act as catalysts to particular chemical reactions occurring in the soil. These enzymes have varying functions but most help the plant to absorb nutrients or stimulate new root growth. Scientists have discovered that when additional carbohydrates are added to a soil or hydroponic feeding program the result is an increased population of beneficial microorganisms which leads to an increase in the beneficial enzymes they produce as by-products.

Enzyme Additives

Recent innovations in extraction methods have allowed scientists to not only identify specific beneficial enzymes but to also isolate them. This has led to some of the most incredible organic products to hit horticulture: enzyme additives. As previously mentioned, enzymes are powerful catalysts that accelerate chemical reactions occurring in the soil. By isolating particular enzymes, scientists are able to create enzyme formulations with very specific purposes. For example, by isolating an enzyme that promotes new root growth and creating a formula with a high concentration of this particular enzyme, the result is an extremely powerful organic root stimulator. Other specific enzyme additives on the market are used to convert dead root matter into usable nutrients for the plant. As you can imagine, these additives are great for general maintenance in hydroponic gardens and can also be used to aid the cleaning process of hydroponic systems.  As scientists learn more about the functions of individual enzymes, we will see more organic enzyme additives enter the marketplace, each with a specific function (e.g., aid in the absorption of a particular essential element). Enzyme additives could be the key to growing crops in unbalanced soils as the enzymes could aid in the absorption of the nearly depleted nutrients.

Amino Acid Additives

Amino acid additives are another example of what can be obtained by way of innovative extraction techniques. Amino acids are everywhere in our gardens. Our plants are continuously generating amino acids and they are constantly affecting every plant function in our gardens and greenhouses. This is because amino acids are used for the synthesis of cellular molecules, including chlorophyll, enzymes, proteins, and vitamins. Life as we know it would simply not exist without amino acids. Plants grown in perfect conditions will create enough amino acids to function properly. However, most hobby greenhouses are suitable for plant growth but are far from providing optimal growing conditions at all times. By supplementing amino acids, horticulturists can ensure the plant’s metabolism continues to operate at full-tilt, even during times of stress. Plants given additional amino acids have shown higher resistance to all environmental and pathogenic stresses. There are two types of amino acids: D-form and L-form. Amino acid additives for horticulture are L-form amino acids and are sold in liquid form.

Hobby greenhouse growers who want to grow organically have more than enough options to choose from. Organic fertilization can be as simple as amending your soil with a variety of individual ingredients in granular form or as complex as using multiple liquid organic fertilizers throughout the plant’s life cycle. Whether the gardener chooses granular or liquid organic fertilizers, they can supplement with any or all of the non-nutrition additives. The microscopic world of beneficial microorganisms is the essential link between plant and organic nutrition. Regardless of the methods or products used, the main goal of the organic gardener should be to encourage the symbiotic relationships in the soil to flourish. After all, sometimes the smallest creatures can make the biggest difference in our greenhouses. This is most certainly true for the organic horticulturist.

Eric Hopper resides in Michigan’s beautiful Upper Peninsula where he enjoys gardening and pursuing sustainability. He is a regular Garden & Greenhouse contributor and may be contacted at

Want more information? Read these articles:

Brushing Up on Your “Fertilizer-Speak”

Calcium: The Forgotten Fertilizer

Dry Fertilizers vs Liquid Fertilizers

Fertilizer 101 by the Numbers

How to Use Foliar Fertilizers for Fantastic Plants

The Fertilizer Value of Worm Castings

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One thought on “Organic Fertilizer Overview”

  1. Ashley Maxwell says:

    Thanks for your comment about how organic fertilizers are made out of blends with elements such as potassium and nitrogen that help plants and fruit grow healthily. I didn’t know that they can be put in the soil before planting as well as after. My mom has a garden and she wants her plants to be healthy as they grow, so she is considering organic plant nutrients.