What Are Marijuana Plant Hormones?

marijuana plant hormones homegrown
April 20, 2020

Most home growers don’t know a great deal about plant hormones and how they influence growth. Maybe you’ve heard about them in passing but you’re not entirely sure what they do or how you can manipulate them to grow better cannabis plants.

Hormones are naturally occurring molecules that play a critical role in growth and other functions. In addition to controlling temperature, humidity, pH, light, airflow, carbon dioxide and nutrients, you can also strengthen plants by understanding their hormones and how they work.

Marijuana Plant Hormones: Everything You Need to Know

Plant hormones – also known as phytohormones – are naturally occurring molecules that regulate all aspects of plant growth and development. Throughout a plant’s life cycle, they can slow or speed up growth and facilitate vital processes and functions. More than that, phytohormones can also impact how plants respond to external factors including environmental stress, physical damage, and exposure to pests and pathogens.

The 5 Major Types of Natural Plant Growth Hormones

Plant hormones can be classified into five different types: abscisic acid, auxins, cytokinins, ethylene, and gibberellins.

How phytohormones affect cannabis plants:

Seed dormancy Seed germination Vegetative Phase Flowering Phase
Abscisic acid Yes Yes


Yes Yes Yes

Yes Yes



Yes Yes Yes

1. Abscisic Acid

Abscisic acid (ABA) inhibits growth (in a positive way) and regulates transpiration, helping plants deal with environmental stress factors, pests and pathogens. It’s basically the hormone that shuts things down when things get bad.

Abscisic acid promotes dormancy in both seeds and buds, preventing plants from germinating in wintry or adverse conditions (when survival chances are low). As winter approaches, it acts to slow down growth so the plants can prepare for the upcoming cold.

ABA is also produced during drought conditions to stop the plants from developing new leaves. It closes the stomatal pores to halt transpiration, reducing the amount of water that can evaporate from the leaves. This helps prevent the plant from wilting or dying during periods of intense heat and dryness. For this reason, abscisic acid is often labelled an anti-drought or stress hormone.

2. Auxins

Auxins are a group of hormones that help control the formation and growth of roots, leaves and flowers. They can be used to encourage rooting or as a general growth stimulant for vegetating plants. There are many types of auxins, but the most important is indole-3-acetic acid (IAA).

High concentrations of auxin can help with cell wall plasticity, allowing plant cells to stretch and grow. As the cells enlarge and elongate, so do the tissues and organs (resulting in bigger buds). Keep in mind, though, that excessively high doses can impede, rather than promote, cannabis plant growth.

Auxins are responsible for phototropism, which causes the plants to bend towards the light source, and geotropism, which stimulates downward root growth in response to gravity. They also promote apical dominance, inducing vertical plant growth with the largest, tallest, and most prominent bud at the top.

Without auxins, the plant wouldn’t be able to grow, stretch or expand beyond a seedling. We have a lot to thank them for!

3. Cytokinins

Unlike other hormones, cytokinins are present in both animals and plants. There are many types, with zeatin being the most widespread. Typically, they are used as a growth stimulant during the vegetative stage to promote thicker, sturdier stems and branches, and during the flowering stages to produce denser buds.

Cytokinins are involved in cell division and cell growth. They are also involved in other functions such as the development of adventitious roots, axillary buds and leaves. You can improve and increase yields by taking advantage of their senescence-delaying effect (the slow-down of aging).

The cytokine-to-auxin ratio determines how plant growth is affected as these two hormones interact synergistically. A low ratio is ideal for vegetative growth as it encourages root development. A high ratio triggers the flowering phase and produces more shoots. Commercial products usually contain specific blends to induce a plant to grow in a certain way.

4. Ethylene

Ethylene is a flammable gas that promotes ripening and senescence, sometimes referred to as the aging hormone. It is involved in epinasty and abscission, the mechanics behind drooping and dropping leaves. Its other functions include seed germination, phototropism and flower development.

Plants typically produce more ethylene as they age or as a response to stress or injuries. Excessively high levels can be damaging, causing the plant to perish rapidly. Since ethylene counteracts some of the effects of auxin, it’s important to maintain a balance between the two hormones.

5. Gibberellins

Of the several types of gibberellins, gibberellic acid (GA) is the most commonly used. This multi-tasking hormone is involved in an array of metabolic functions. Using it as a general stimulant, it helps germination by breaking seed dormancy. Throughout the growth stages, it encourages stem elongation and extensive root development. More importantly, it also helps enhance trichome production and bud growth as well as protecting the plants from environmental stress.

A shortage of gibberellins can lead to stunted growth. An excess, on the other hand can lead to the formation of weak, lanky stems that may not support the plants. When used correctly, growers can expect a prolific harvest of large, hefty buds.

Other Types of Phytohormones

Aside from the five listed above, here are other common plant hormones.

Seed dormancy Seed germination Vegetative Phase Flowering Phase

Yes Yes


Jasmonates Yes Yes Yes Yes
Salicylic acid



Yes Yes
  • Brassinosteroids. These are a class of plant steroid hormone that regulate thousands of genes inside the cell. Brassinolide is the most widely known and works best with auxins and gibberellin. Among its most important functions are boosting growth, encouraging seed germination, gravitropism, phototropism, and ethylene production.
  • Florigen. This plant hormone is naturally produced as the days turn shorter and the nights grow longer. Because it helps trigger flowering, it is dubbed the flowering hormone. Indoors, you can manipulate the light cycle to promote florigen production, helping the plants bloom and thrive. If growing outside and light is scarce, you can use florigen supplements.
  • Jasmonates. These lipid-based phytohormones regulate several plant processes, including growth, photosynthesis and reproductive development. Jasmonates have many derivatives, each of which has its particular uses. For instance, jasmonic acid helps with germination, seedling growth, root formation and budding. Methyl jasmonate assists in seed germination, root growth, plant defense, and flowering.
  • Salicylic acid. Originally isolated from willow bark extract, salicylic acid helps plant growth and development, photosynthesis and transpiration. It also plays a crucial role in defense, increasing resistance to pathogens and helping with the abiotic stress response, reducing the need for pesticides.
  • Triacontanol. This fatty alcohol can help boost plant growth and development as well as increase yields. It can be used right through a plant’s life cycle – from seedling to harvest. It works in conjunction with auxins, cytokinins, gibberellins and brassinosteroids.

Plant Hormones vs. Growth Regulators

The primary difference between the two is that plant hormones are naturally occurring. In contrast, plant growth regulators (PGRs) are synthetic or man-made. An example is indole-3-acetic acid (IAA), which is typically sold as indole-3-butyric acid (IBA) and 1-naphthaleneacetic acid (NAA). IBA and NAA closely resemble the structure of IAA, allowing them to mimic its effects. There is also kinetin, an artificial cytokinin.

You may have heard that plant growth regulators are harmful and should be avoided at all costs. This is only true to a certain extent. PGRs can be derived naturally or chemically. As you might have guessed, PGRs laden with chemicals are the ones to avoid.

Why Avoid Chemical-Based Plant Growth Regulators

If the buds are covered in brown hairs and lacking in trichomes, with little to no smell, they might have been exposed to chemically-derived PGRs. The sole reason for using PGRs is to increase yields, which, in turn, helps bring in more profit. This can come not only at the expense of the plants but humans and the environment, too.

Chemical PGRs don’t just replicate the effects of phytohormones but they also act upon them, interfering with their production and breakdown. As a result, they can prevent or slow down growth, as opposed to other PGRs which work to stimulate growth. For this reason, chemical PGRs are sometimes called plant growth retardants.

PGRs skyrocket yields by cellular expansion through the signal transduction pathways. Upon activating the plant growth hormones, they cause the plant cells to enlarge, allowing them to absorb and hold more water. Doing so results in denser and fatter buds but severely compromised quality and potency.

Many PGRs – including daminozide, paclobutrazol, chlormequat chloride, and uniconazole – have also been implicated in liver damage and the development of cancers and tumors. Some are even considered to be pesticides. They can destroy the soil’s microorganisms and harm marine life when released as run-off.

Plant Growth Retardants to Avoid

PGRs are available commercially in different brand names. The most common active ingredients – and also the ones to stay away from – include:

  • Ancymidol
  • Chlormequat chloride
  • Daminozide
  • Ethephon
  • Flurprimidol
  • Paclobutrazol
  • Uniconazole

Daminozide and paclobutrazol, in particular, are a cause for alarm, as these are present in some cannabis fertilizers, but are not listed in the ingredients list. Paclobutrazol may also interfere with terpene production.

What Are Rooting Hormones?

Rooting hormones – also known as rooting stimulants – are probably the most well-known and most widely used marijuana plant hormone products. They typically contain synthetic auxins like IBA and NAA. They are commonly applied to cannabis cuttings to help them take root. They can also be used on seeds and seedlings to promote healthy, vigorous rooting. Simply put, rooting hormones allow growers to propagate quickly and successfully while ensuring robust and sturdy roots.


Rooting hormones are available in three different types – liquid, powder or gel. Each has its pros and cons, especially when it comes to the application method. As always, it all comes down to need and preference.

  • Liquid.This type is versatile and is supplied in concentrated or ready-to-use form. Concentrated rooting hormone needs to be diluted before use, allowing for customization of the dose and ratio as desired. On the other hand, ready-to-use products are more convenient. To use, dip the cuttings into a cup full of the cloning solution for at least five seconds then transfer to the substrate of choice.
  • Powder. This form is commonly used by commercial growers or those planning to raise several crops. Of the three, the powdered type has the most extended shelf-life. It is also cost-effective since a tiny amount can help several clones take root. To use, simply dip the cutting into water, then into a bottle cap or a small container filled with the powder. Afterward, gently tap it off to get rid of the excess, then plant the trimming in the preferred growing medium.
  • Gel. This type is often used by indoor cannabis growers. As the name suggests, it has a thick, gooey consistency. The gel is convenient and easy to use, allowing you to cover the entirety of the stem. To use, place a small amount of the gel on a container, dunk the clone into it then move it to the chosen medium.

When and How to Use Marijuana Plant Growth Hormones

Marijuana plant hormones should be used sparingly and only as needed. In most cases, this is when plants transition to a new growth stage or when you are trying to address specific problems. Keep in mind the dosage and the appropriate hormone to use and carefully read the supplied instructions.

Propagating Clones

When propagating clones, rooting hormones are a necessity. They are typically applied to the tips of the stem cuttings before moving them to the preferred rooting medium.

Some of the most recommended products include:

Whatever the choice, never dip the cutting directly into the product bottle. It is unhygienic and can spread disease and infection.

Seed Germination

Our quick video guide to cannabis seed germination

Applying small amounts of gibberellic acid can help cannabis seeds break free from dormancy, allowing them to germinate faster. It is particularly useful for old, dried out ovules that are struggling to sprout roots. Gibberellic acid is exceptionally potent, so a little goes a long way. Ideally, about 2 ppm of the hormone will do. Soak the seeds in diluted gibberellic acid, or use the solution to germinate the seeds via the paper towel method.

Seedling Stage

Some cannabis growers use rooting hormones to promote healthy, vigorous root development. One option is to add a bit of cloning powder to the potting mix to make it richer in auxins. This is only recommended when starting with solo cups or a small container. Otherwise, the auxin content might inhibit stem development, resulting in stunted growth.

Alternatively, you can also mix a small amount of cloning liquid with water, using it to irrigate the seedlings immediately after transplant. This approach prevents the auxins from building up in the medium, which means that it will not slow down stem growth later on.

Vegetative Stage

During the vegetative phase, the goal of hormone application is to stimulate overall growth and development. The roots, stems and leafage are, in particular, of primary concern. Plant hormones like auxins, cytokinins and gibberellins are suitable. These are typically used as a foliar spray or combined with water to drench the medium.

Keep in mind, though, you are not limited to these three hormones.

Marijuana Plant Hormone Helps with the Following Processes
Auxins Root growth, formation, and expansion Leaf formation Stem elongation Overall growth 
Cytokinins Root development Formation and development of stems and branches Leaf development Leaf expansion Overall growth 
Gibberellic acid Root development Stem elongation Overall growth 

Flowering Stage

For the final growth stage, the aim is to promote flower production and to increase yields. In that regard, auxins, cytokinins, ethylene, and gibberellins are the most beneficial. They can be used as a foliar spray or applied to the roots by mixing it with water then using it to flood the medium.

Marijuana Plant Hormone Helps with the Following Processes
Auxins Formation of flowers Enlargement of flowers
Cytokinins Bud development Bud productivity
Ethylene Flower development
Gibberellic acid Bud development Trichome production Enlargement of flowers Bud productivity

Using Plant Hormones to Maximize the Potential of Cannabis Plants

Plant hormones are all-around molecules that can impact cannabis growth and productivity in many ways. They are versatile and can be applied from germination to flowering. To know which one to use, it’s important to have a basic understanding of the most common hormones – especially their functions.

Keep in mind, though, there is little research on the effects on phytohormones – be they naturally occurring or man-made – on cannabis plants. As such, you may have to experiment to see which hormones work best – including the ratio, strength, mode of application and frequency of use, depending on your needs. Strain and growing environment can affect how these hormones act upon the plants.

At any rate, the effort is more than worth it. With patience and careful dosing it will not be long before you witness the plants growing vigorously, reaping an abundant harvest of high-quality buds.