When done correctly, cloning Cannabis can be a cheap and effective way to populate your production rooms.
However, when it goes wrong, cloning can become an arduous and frustrating task. Given the increasing price of materials and labour, a failure to root can also be an expensive
Fig.1: A fully rooted Cannabis clone in "Grodan Max" the latest in stonewool technology from Grodan. Source: Big Leaf Consultants.
One of the most common techniques for propagating Cannabis i.e producing more plants from existing plants, is cloning.
Cloning is an economical way to produce a continuous supply of predictable plant material for commercial batches.
When done correctly it can yield an innumerable number of additional plants and can be much cheaper than using seeds.
Cloning is particularly relevant in the medical Cannabis industry since unlike propagation through seeds, it ensures all plants are genetically identical - the first step in attempting to standardise the resulting pharmaceutical product.
What is a Cannabis Clone?
Simply put, a Cannabis clone is a genetically identical cutting that is removed from the growing shoots of a donor mother plant.
Donor mother plants are maintained in a vegetative state meaning they are exposed to at least 18 hours of light.
This ensures they grow mainly roots, stems and leaves and don't produce flowers. This generative process is instead triggered through a reduction of the photoperiod from 18 to 12 hours of light.
How is Cannabis Cloned?
In practical terms, cloning is an easily taught technique that can differ slightly from grower to grower but ultimately the overarching concept is the same.
The youngest growth of a donor mother plant is pruned off to yield cuttings. These can be anywhere from 10-20cm depending on the facility and growing style.
Once pruned and once excessive biomass is removed from the cutting, clones are prepared for "plugging" into a rooting substrate by dipping in a rooting agent - typically synthetic rooting hormones.
Commonly used substrates in the medical Cannabis industry are rockwool and peat plugs. Increasingly many facilities are turning to rockwool due to its completely inert nature and absence of organic matter.
Over the next 7-21 days cuttings are carefully monitored and temperature, relative humidity and lighting are controlled. During this period new roots should appear.
Many facilities employ the use of propagation domes to maintain high humidity during the critical first few days to prevent wilting and transpiration stress (Fig.2).
Fig.2. A propagator consists of a tray, insert and dome. The main purpose is to provide a high humidity environment for newly plugged cuttings. Source:cannapages.com
8 Tips for Cloning Success
Once again, although simple in theory, the practice of taking and maintaining clones has various inherent risks which can ultimately compromise the success rate of the process.
The proof of a successful cloning event is the development of a healthy root system evenly covering the substrate plug within 21 days. Any longer just wouldn't be viable from a production point of view.
Over the years we have witnessed various obstacles to successful rooting. Luckily, many mistakes are repeated among novice teams and improvements can be narrowed down to seven essential tips.
1. Only Clone Healthy Mother Stock
The absolute golden rule for cloning has to be starting with healthy donor mother plants. Since cuttings are genetically identical to the plant they are removed from, any pests or pathogens or nutrient issues that are plaguing the mother plant will be conserved in any material that is removed from her.
Cloning a healthy plant also gives you the best starting chance of success given the vulnerability cuttings have due to lacking a developed root system. Clones taken from a sickly plant will also be less likely to root since their growth and subsequent development will be compromised.
Ensuring your mothers are free of pests and diseases, show a good healthy green colour and vigour and are well-watered is the first step towards rooting success.
If cloning from seed plants - ensure you are definitely cloning a female plant. Ideally, before cloning anything at scale it's a good idea to have an idea of what the plant flowers like to make sure you have a desirable phenotype worthy of cloning in the first place.
2. Size it Right - Cutting Diameter, Length & Leaf Number/Size
If your goal throughout the growth cycle is a homogenous canopy in order to ensure a uniform final product then the first step in this process begins at propagation.
Choosing cuttings that are roughly the same diameter and cutting clones to a specific height is an important but often overlooked characteristic of proper commercial cloning.
Ensuring your staff are trained in size guidelines also helps to develop procedures for rejecting material not suitable for cloning. Generally, clones that are thinner in diameter may represent material that is underdeveloped and less likely to survive the stress of cloning.
Material that is too thick or "woody" could also take longer to root so isn't a good candidate for cloning.
Leaf number is also an important factor. Cuttings that are too bushy will create overcrowding and trays and support the formation of micro-climates within the propagator. This increases the risk of mould and mildew.
Some growers will trim leaves to reduce the surface available for transpiration and reduce crowding. However, some of the only published research on Cannabis propagation found that leaf trimming reduced rooting success from 71%-53% whilst clones with three fully expanded leaves rooted faster than those with two (Caplan et al 2018). The use of cell-spacing trays prevents overcrowding and could allow growers to test the findings of this study for themselves.
Another study on Cannabis propagation found that stem wounding increased rooting by 162% and accelerated rooting by 1.5 days compared to unwounded (Campbell et al 2019). This practice requires careful expertise however and can significantly slow down a cloning process. Before adopting it as part of your internal procedures be sure to test this technique out for yourself and ensure you test its success on each of your commercial strains.
Depending on your facility the length of cuttings should be determined by factors such as ceiling height, vegetative time, plant density and equipment such as propagator size.
A final bonus tip we will squeeze into this section is contingency - always cut more clones than you need to fill a room to ensure you have enough if some inevitably don't make it. Standard practice suggests 20% extra. This can be reduced as your process improves and as you get better acquainted with the specific behaviour of your commercial strains.
3. Test Your Source Water
This tip is particularly important for those growing hydroponically - which is most producers in the medical Cannabis industry.
Testing your source water is an essential part of the facility design process and integral to maintain on a regular basis once you are up and running. Knowing your starting pH and EC is critical for developing fertigation protocols.
Deciding on water purification technologies is also dependent on this data which can also provide a full assessment of the nutrient profile of your source water as well as identify any areas for concern such as water hardness and microbial contamination.
Aside from being an integral medium for the transportation of nutrients, water can also transport less desirable things including microbial organisms that can spread diseases.
Root rot-causing pathogens including Pythium and Fusarium are water-borne and can wreak havoc on delicate clones. Keeping your system clean is also integral for preventing the build-up of biofilms that are known to harbour root-rot-causing pathogens.
If necessary various options exist for purifying your source water to make sure your fertigation system isn't the source of cloning failure. Slow-sand filtration, Ozone, UV, chlorine dioxide gas injection, Electro Chemical Activated water (ECA), nanobubbles and reverse osmosis are just some of the available options.
4. Known Your Substrate
Understanding how to use your substrate is integral for properly preparing and managing it as part of cloning procedures.
Depending on the chosen substrate, some suppliers provide ready-to-use options that don't require hydrating. With these options, it's important to note if substate plugs already contain nutrients so as to not over-supply these and risk nutrient stress.
Other substrates like rockwool require careful preparation with recommended pH and E.C ranges. Using the wrong pH and EC will compromise your clone's health from the get-go and could result in failure due to nutrient stress which will ultimately prevent the development of a root system.
Ensuring a tight fit between your cutting and the substrate is also important for reducing the risk of air bubbles in the stem and ensuring cuttings stay upright and don't fall over.
Some cloning plugs may require gentle moulding around the clone after it has been plugged whilst others come pre-perforated. However, depending on the diameter of your cuts it may be better to choose an unperforated substrate and punch customised-sized holes in yourself.
5. Use a Rooting Hormone
Rooting hormones are commonly used on a variety of plants across the horticultural industry to promote the growth of roots but also flowers and fruits. Depending on your location-specific rules will determine exactly which products can be used for e.g in Portugal only "Rhizopon" is registered for use in medical Cannabis while more well-known brands such as "Clonex" are not.
Plants naturally produce a number of different hormones that regulate functions including growth, stress response, pathogen resistance, senescence (ageing), abscission (the shedding of leaves, flowers and fruits) and germination.
Auxins are the category of plant hormones that control cell enlargement, bud formation and rooting. The most commonly occurring auxin is Indole-3-acetic acid (IAA).
Many synthetic rooting agents contain Indole-3-butyric acid (IBA), another naturally occurring auxin.
Although rooting is possible in the absence of hormones, it can be significantly slower depending on the specific technique used. The same propagation study that evaluated the impact of leaf trimming also found a 0.2% IBA gel was more effective than a 0.2% willow extract gel at stimulating rooting (Caplan et al 2018).
Some growers swear by deep water culture cloning where rooting takes place with cuttings suspended in an aerated nutrient solution. Others may choose to omit synthetic hormones and use naturally derived rooting agents such as willow bark or aloe vera.
When working with rooting hormones it's important to pay attention to the strength of the hormone and resist the urge to over-apply since this could in fact delay rooting by causing burning or dehydration of plant tissue (Cerveney and Gibson 2005).
6. Maintain an Ideal Environment & Acclimatise Clones Gradually
Ensuring your clones are exposed to the correct range of temperature, relative humidity and light intensity is another method towards achieving rooting success.
In order to reduce transpiration stress and to make up for a lack of root system clones should be exposed to high relative humidity. Particularly in the first few days of rooting this should be maintained above 90% where possible and can gradually be reduced to accommodate rooting progression.
Your cuttings do not require the same light intensity as other plants in the vegetative state and could stress out if the lighting is too high. LED fixtures are ideal for lighting cuttings since they can be placed close to the canopy without the risk of over-heating and burning.
Acclimatisation refers to the process of slowly exposing your clones to conditions similar to the environment they will be transplanted into once they leave the cloning room i.e. the vegetative room. From this point onwards plants are generally exposed to lower relative humidity and higher light intensity. Many facilities also maintain temperatures slightly lower than their cloning environment. Acclimatisation decreases the chances of your clones stressing when they are transplanted and is a way to ensure a smooth transition into the next growth phase. Transplant shock can range from a few hours to days and even weeks.
Remember, any time your plants spend in recovery is time they don't spend growing.
7. Water Carefully
Ensuring a high humidity environment is a means with which to reduce transpiration stress on clones during the first critical phase of their rooting.
A common mistake is an absence of an irrigation procedure that is based on achieving a certain amount of dry back before scheduling a watering event.
Over-watering is as problematic as under-watering but for different reasons.
Fungal pathogens flourish in high moisture environments and giving your clones water before they require it can lead to over-saturation of the substrate, reduced oxygen in the root zone and outbreaks of mould.
Knowing your substrate is critical to understanding how to properly hydrate it and developing an irrigation strategy based on a specific dry-back is an invaluable tool for training staff in responsible and effective watering strategies.
If in doubt remember the golden rule "transpiration before irrigation," meaning, be sure your substrate has lost a certain amount of weight, and therefore water, before re-wetting. This can be done by weighing but also by careful observation of the above-ground plant biomass. Train staff in symptoms of drought-stress so these can be used in conjunction with more easily quantifiable measures such as substrate moisture content.
8. Keep it Clean!
We've saved one of the most important points until last. Good hygiene and sanitisation practices are of fundamental importance to cloning success.
Young clones are particularly vulnerable to pest and pathogen attacks due to the compromised stress and immune response that comes from an underdeveloped root system.
Any cultivation techniques that use a recirculating irrigation system should ensure regular cleaning of the entire system to prevent the build-up of biofilms and their water from becoming a source of contamination.
Sanitising tools used during cloning events is a vital step in preventing the spread of potentially devastating diseases including Hop Latent Viroid. For more in-depth information on this pathogen read our article here.
An over-reliance on products such as isopropyl alcohol (IPA) and hydrogen peroxide won't achieve the success of a diluted bleach solution or a virucide in ensuring environments are free of viral contamination.
Proper cleaning of equipment including cloning trays and domes should be done between every use. Clean equipment should be stored in a separate area to used equipment and ideally labelled with a cleaning expiry label to ensure re-usable items stay contamination free.
Cloning Cannabis doesn't have to be hard.
Once good practice and procedures are in place a good genetic should regularly give rooting success rates of over 90%.
Whilst this list is by no means exhaustive, paying close attention to these eight tips will prevent your facility from committing some of the most classic mistakes in the industry.
Although knowing the theory behind how to successfully clone Cannabis is a valuable first step toward rooting success, nothing beats on-hand practical training. Our team offer a range of in-person training designed to teach your cultivation staff industry-standard techniques to set them on the road to success.
Get in touch with Big Leaf Consultants today to learn more about our other cultivation-focused training services and learn more about how we can optimise your processes.
Campbell, L. G., Naraine, S. G., & Dusfresne, J. (2019). Phenotypic plasticity influences the success of clonal propagation in industrial pharmaceutical Cannabis sativa. PloS one, 14(3), e0213434.
Caplan, D., Stemeroff, J., Dixon, M., & Zheng, Y. (2018). Vegetative propagation of cannabis by stem cuttings: effects of leaf number, cutting position, rooting hormone, and leaf tip removal. Canadian Journal of Plant Science, 98(5), 1126-1132.
Cerveny, C., and Gibson, J. (2005). Grower 101. Rooting Hormones. Available at: