Garden & Greenhouse


Enzymes, Amino Acids and Plant Hormones

Posted February 15th, 2017 by Eric Hopper in ,

A good feeding regiment will contain all the essential elements and trace minerals needed for healthy plant growth. In addition to these vital nutrients, many horticulturists choose to “super charge” their feeding programs with non-plant food additives. These additives are not actually nutrients, but are additives which enhance plant growth or increase efficiency in various ways. Three of the most popular non-plant food additives used by indoor horticulturists and greenhouse hobbyists are enzymes, amino acids, and plant hormones.


In nature, beneficial microorganisms produce a wide variety of enzymes that have been shown to accelerate plant growth. There are chemical reactions happening constantly within the soil. The role an enzyme plays in these reactions is unique because the enzyme itself is not responsible for the reaction, but rather the speed at which it occurs. In this way, enzymes become a biological regulatory system for many of the chemical reactions that affect plant life.

Enzymes are highly selective catalysts made up of amino acids, proteins, or RNA.  Enzymes differ from other catalysts in their selective nature. In other words, enzymes only react with a specific, predetermined substrate. When enzymes are formed they take on a certain shape which ensures that only specific reactions can occur. Like other catalysts, enzymes are able to increase the speed of chemical reactions by lowering the activation energy required for the given reaction. Put another way, when a horticulturist uses enzymes in his or her feeding regiment, it will help accelerate the rate at which nutrient absorption occurs.

How to Supplement Enzymes

A horticulturist can supplement enzymes into his or her garden directly or indirectly. Using a liquid enzyme formula that is comprised of the isolated enzymes is an example of direct enzyme supplementation. Supplementing beneficial microorganisms which, in turn, increase the amount of enzymes in the medium is an example of indirect supplementation. Either method should be used in conjunction with a complete fertilizer regiment.

Amino Acids

Amino acids are organic compounds with an amino (-NH2) and a carboxylic acid group (-COOH) and are required for plant functions throughout the plant’s entire life cycle. Amino acids are used for the synthesis of cellular molecules, including chlorophyll, enzymes, proteins and vitamins. Amino acids begin their vital roles at the very beginning of a plant’s life. During the germination process, an embryo will consume amino acids derived from proteins stored in the endosperm. After that, amino acids will affect the plant’s metabolism in many ways. They are directly linked to vital plant functions, including the synthesis of structural proteins, contributing to the formation of plant hormones and the regulation of water. When necessary, amino acids can even act as chelators of the essential nutrients required for healthy plant growth.

Plants grown in absolutely perfect conditions will create enough amino acids on their own to function properly. However, most plants are not grown in absolutely perfect conditions. By supplementing an amino acid formula into a feeding program, a horticulturist can ensure his or her plants will always have access to a sufficient amount of amino acids. That way, when the growing conditions falter, the plants will have a better chance of remaining on track.

Types of Amino Acids

There are two types of amino acids: D-form and L-form. The D-form amino acids are larger molecules that cannot be used by plants. This is why any amino acid formula designed for horticultural use should be comprised mostly, if not entirely, of L-form animo acids. L-form amino acids, in the free form or in formation with small peptides, can be absorbed and used by plants.

Plant Hormones

Phytohormones, also known as plant hormones, are specific chemicals which regulate the growth processes of plants. Plant hormones affect a wide variety of functions, including the formation of stems, leaves and roots, as well as the initiation and development of fruits and flowers. Plant hormones are classified based on their molecular structure. The five major classes of plant hormones are auxins, gibberellins, cytokinins, abscisic acid and ethylene.


Auxins are the plant hormones associated mainly with physical structure. These hormones stimulate upward growth, suppress side branching and stimulate root growth. Perhaps the most widely known effect of auxins is tropism (plants moving toward the light source). It is the concentration of auxins on the shaded side of the stem that stimulates cell elongation which then turns the stem toward the light source. Auxins are transported cell to cell through a complex and organized process known as polar auxin transport. It is this intricate transporting of plant hormones that allows plants to react to external conditions without requiring a central nervous system.

Using Auxins in Horticulture

For the indoor horticulturist and greenhouse hobbyist, auxins are most commonly used in rooting concentrates. Rooting gels or solutions designed for propagation usually contain at least one and, many times multiple, auxins. These particular auxins help initiate root growth and aid in root establishment. Some of the new, innovative products that utilize auxins are focused on increasing vegetative growth and manipulating the structural integrity during the fruiting and flowering stage.


Gibberellins are the plant hormones connected with developmental processes, including germination, dormancy, establishing sex, flowering and leaf and fruit senescence. Gibberellins are specifically involved in breaking dormancy and multiple aspects of germination. The breaking down of stored starches in the endosperm begins when the seed is exposed to moisture. It is believed that gibberellins trigger the synthesis of the enzymes that are responsible for breaking down stored starch into usable glucose.

Using Gibberellins in Horticulture

Gibberellins are often used in horticulture to stimulate flowering, alter sex and initiate germination. Since many hormones fit in the classification of gibberellins, their use in horticulture is widespread. In some cases, horticulturists will use a hormone antagonist instead of the hormone itself. Paclobutrazol is a well-known antagonist to gibberellins and is commonly used on ornamental plants to slow growth and induce early flower production.


Cytokinins are the plant hormones associated with cellular division. These hormones are also associated with embryo development, seed germination and flower development. The amount of auxins present will affect the way cytokinins function and vice versa. In other words, the ratio of cytokinins to auxins directly affects the way each hormone influences plant growth. For example, if there are more cytokinins than auxins, the growth of shoot buds will be stimulated. However, if the ratio contains more auxins than cytokinins, root formation will be stimulated.

Using Cytokinins in Horticulture

Cytokinins are popular in modern horticulture as both growth and flower stimulators due to their stimulation of cell division. Foliar applications of cytokinins during the early weeks of the flowering stage will increase fruit or flower sites which leads to higher yields for most indoor horticulturists. Some cytokinins have even been shown to increase a plant’s pathogenic resistance. In the future, this could lead to hormone treatments that would help monoculture crops be more resistant to pathogens.

Abscisic Acid

Abscisic acid is the plant hormone most associated with stress. This hormone is synthesized by plants in response to environmental stresses. For example, in times of decreased soil moisture, the abscisic acid produced by the roots is translocated to the leaves where it rapidly causes the stomata to close. This reduces further loss of moisture through transpiration and protects the plant from suffering additional damage from drought. For perennial plants, abscisic acid plays a vital role in bud dormancy during the winter months. As the cold weather approaches, abscisic acid is produced by the plant to slow down plant growth and help form a protective barrier around the dormant buds.

Using Abscisic Acid in Horticulture

The most common use of this hormone in indoor horticulture is in anti-wilting solutions. During the propagation process, growers can spray their cuttings or seedlings with a solution containing abscisic acid which will close the leaves’ stomata. This allows the cuttings or seedlings to withstand lower humidity conditions without wilting due to moisture loss through transpiration.


Ethylene is the plant hormone related to stimulating and regulating the ripening process. Aside from ripening, ethylene has also been shown to be influential in the opening of flowers and the shedding of leaves. The production of ethylene is regulated by environmental and developmental factors. Environmental stresses, including flooding, drought, frost, or pathogenic attack, can stimulate ethylene production.

Using Ethylene in Horticulture

Ethylene has been used in horticulture since the ancient Egyptians deliberately damaged their figs in order to stimulate ripening (a process which stimulated ethylene production). Presently, catalytic generators create ethylene gas in commercial chambers designed to ripen fruits and vegetables. Ethylene causes a delayed flowering response in some plants, including chrysanthemums. Some chrysanthemum growers will deliberately raise the ethylene concentration in their greenhouses to slow the flowering process when necessary.

Many professional horticulturists use enzymes, amino acids and plant hormones to stimulate growth, increase production and even promote ripening. Indoor gardeners and greenhouse growers can also reap the vast benefits of supplementing these non-plant food additives into their gardens. Successful gardening takes a multifaceted approach and, in order to optimize growth, horticulturists need to supply their plants with more than just the basic essential elements. Growers who “super charge” their feeding regiments with the addition of enzymes, amino acids, and plant hormones are sure to increase their likelihood of success. Aside from creating an increased resistance to pathogens, better stimulation of plant functions and increased efficiency, experimenting with non-plant food additives is a great and fun way for a gardener to expand their knowledge of horticulture.

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

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