One of the first things new gardeners will notice as their plants begin to progress and require food is that there are plenty of nutrient additives out there to choose from. When deciding which additives to include in a feeding schedule, knowing what you are adding and why you are adding it is much more important than how pretty the label is or how catchy the name sounds.

Here, in alphabetical order, are some of the more common nutrient additives you may see listed on the products available at your local hydro store, and what purposes they serve in the garden.

Abscisic acid (ABA) aids in a plant’s resistance to drought and is instrumental in triggering and maintaining dormancy in seeds and plants.

Acetylsalicylic acid (ASA, aspirin) treatments induce systemic acquired resistance, a whole-plant resistance response that can help plants become more resistant to and fight off pathogens.

Anti-gibberellins are “chemical pinchers” that retard plant growth height and often inhibit gibberellic acid development, which promotes growth and elongation of cells. These growth retardants reduce upward growth in favor of branching.

Auxins such as IAA, IBA and NAA are commonly used in root-promoting products. These hormones promote root growth over leaf development. Natural auxins are made in dominant flowering sites to inhibit the growth of subordinate sites, a process that can be manipulated by pruning. Auxins work in conjunction with cytokinins, either to promote root growth or above-ground development, depending on the ratio.

Bacteria are tiny critters that, along with fungi, work to decompose organic materials so nutrients can be accessible to plants. Aerobic bacteria are oxygen-loving, and need available air to live. Aerobic organic decomposition has a sweet, earthy fragrance. If air is not readily available to the bacteria, then anaerobic bacteria will develop and material will rot, generally venting off foul odors.

Carbohydrates are high-energy foods that encourage microbial growth. While not used directly by plants, the increase in microbial activity can lead to improved plant health and vigor. Cane syrup, maple syrup, fruit juice and molasses have all been used as carbohydrate sources for plants.

Cytokinins are plant hormones that promote cell division in growing shoots. Added to the soil or sprayed on the plants, cytokinins help plants make efficient use of existing nutrients and water in drought conditions. A low ratio of auxins (plant hormones that regulate various functions, including cell elongation) to cytokinins promotes tip and shoot formation. Kelp is one source of natural cytokinins. Cytokinins will counteract the effects of auxins.

Gibberellic acid (GA) is a widely used hormone in the wine and table grape-growing industry to increase production of larger fruit bundles and bigger grapes. GA3 increases plant height, and at levels of 25-100 ppm, encourages masculine flower development on some varieties of female plants. It is also used to help germinate difficult-to-sprout seeds. Over-application of gibberellic acid can lead to tall, stretched plants.

Hydrogen peroxide (H2O2) is both antibacterial and antifungal and can be used to clean water and surfaces of harmful substances such as mold spores. It will kill both the beneficial and baneful organisms.

Humus, fulvic acid and humic acid: Compost is the decomposed remains of plant matter. If compost is allowed to complete the decomposition process, it will eventually stabilize as humus. Humic acid and fulvic acid can be extracted either from humus or from sources such as Leonardite (a soft, waxy, black or brown, shiny, vitreous mineral-like substance that is easily soluble in alkaline solutions).

Indolebutyric acid (IBA), a plant hormone in the auxin family, is an active ingredient in many commercial rooting products. It promotes root growth at the expense of tip growth. A high ratio of auxins to cytokinins stimulates root formation.

Molasses is a by-product of sugar refining and contains not only plenty of carbohydrates to add to your garden, but also potassium, nitrogen and iron as well.

Mycorrhizal fungi are naturally occurring fungi found in plant root systems. Dried spores are added to gardens to encourage the growth of healthy beneficial fungal colonies. These colonies have a symbiotic relationship with the plant, where each benefits more than it loses from the presence of the other. There are two types of mycorrhizal fungi: ecto-mycorrhizal and endo-mycorrhizal. Ecto-mycorrhizal fungi forms on tree roots. For most other plants, including vegetables and flowers, endo-mycorrhizal fungi is predominate. Mycorrhizal fungi thrive on carbohydrates, which is part of what they receive from the plant in exchange for phosphorus.

Naphthaleneacetic acid (NAA) is a synthetic plant hormone in the auxin family. It is included in many commercial rooting products and commonly used to promote rooting. NAA suppresses growth tip development and redirects growing energy to the roots. A high ratio of auxins to cytokinins stimulates root formation.

PK boosts (phosphorus and potassium) are used to increase available phosphorus for use in flowering and fruiting. Mild over-application of phosphorus may initiate a stress response.

Propolis is a fungus mixture honeybees collect and use as a sealant in hives. It is used in the garden as a local antibiotic and antifungal agent.

Silica is taken up by plants and used to reinforce the spaces between cell walls. This mineral skeleton improves plant stability and resistance to some pathogens.

Trichoderma are fungi that colonize the root zone, hopefully outcompeting negative fungi and micro-organisms for resources.

Triacontanol is a naturally occurring plant hormone readily available in alfalfa meal. It encourages cell growth and division.

Zeatin is a cytokinin growth hormone used to encourage growth of tips. Coconut milk is a natural source of zeatin. Zeatin works in opposition to auxins, so they should not be used together.

How to Use Additives in the Garden

Aside from the items on this list, there are plenty of other ingredients growers like to apply to plants, but these are some of the most common. It is important to know not only what is in the additives you use, but also the purpose of using them.

Several of these additives have opposing effects, or are otherwise incompatible. It is often the ratio of the two that causes the effect. For example, ABA and other anti-gibberellins instruct the plant to grow short and squat, but gibberellins tell it to grow tall and lanky.

Using one or the other will initiate the desired effect, but using both at the same time becomes a matter of “which one is yelling the loudest.” Another example of incompatible additives would be the use of H2O2 to sterilize while adding a bacterial or fungal inoculate.

Additives can help a garden flourish if used correctly, and be an unnecessary expense—or worse—if used haphazardly. Take some time, examine your favorite additives, and investigate the effects of their ingredients to help understand not only what to use, but when and why to use it.