In the agricultural world, vegetative propagation (or “cloning”) is remarkably common. Without it, various crops would not be commercially viable, such as bananas, apples, grapes, and sugarcane. Cloning is hugely important in the cannabis industry, as it allows for uniform growth and characteristics, including flavour and effect.
Cloning is imperative to any form of commercial farming, whether it is cannabis, apples or bananas. For some plants, cloning is important because they do not produce a viable seed – Salvia divinorum is one such example. However, in the case of cannabis, cloning allows growers to replicate plants that have ideal robustness, effects and growing habits.
If your circumstances allow it, setting up your own clone room is an invaluable way to maintain and improve your genetic library. However, a good clone room setup is important if you hope to produce healthy clones on a regular basis.
What is cloning?
“Cloning” is the act of cutting a terminal branch (the end of a branch, with a shoot or new pair of leaves at the apex) from a growing plant. The branch clipping is then coaxed into growing roots from the cut stem and effectively becoming a whole new plant.
This ensures all cuttings taken from a “mother” plant will have identical growth characteristics if provided with identical growing conditions. This is because they are “clones” with identical DNA. In terms of cannabis, it means getting the exact flavour and effect required is all but guaranteed—with more certainty than growing from seeds can provide, even with the most stable strains.
The basic process is the same for most plants, but the term “cloning” seems to be cannabis-specific—so if looking for supplies at your local garden centre, referring to your babies as “cuttings” rather than “clones” may be advisable, depending on local laws!
Choosing a mother plant
Choosing a good mother plant is fundamental to the cloning process. There is very little point in essentially immortalising a genetic (or at least massively extending its natural lifespan) unless it has value as a commercial strain.
Growers and breeders typically select mothers on the basis of productivity, height, rate of growth, potency, flowering time, flavour and effect. Other more niche characteristics may also be selected for, such as high CBD levels (increasingly popular in the medical world) or tolerance of cold, for growers in northerly regions.
When growing plants from seed, it is impossible to know what a potential mother will turn out like without flowering it. Therefore, cuttings should be taken from seed plants a few weeks into the vegetative period. These cuttings should then be rooted and immediately placed under 12/12 light to induce flowering. Then, the mothers of the most promising cuttings can be kept permanently in vegetative growth conditions so that more cuttings can be taken.
General set-up considerations
You don’t need much space to set up a clone room. If circumstances dictate, you can even fit out a wardrobe or cupboard to produce several hundred clones every few weeks. Preferably, however, you will have at least a large walk-in closet or small box room of at least 2-3 m2 to work with. Setting up shelves is the obvious way to maximize space, as clones require very little vertical space and can easily be accommodated along with trays and lights in as little as 40cm of height.
Your clone room should be clean and sterile prior to use. If possible, paint the walls with washable paint (white is ideal), and ensure that all surfaces are clean, and can be easily cleaned in future. Make sure that nothing but the essential items are in the room, so that cleaning can be as simple as possible between runs.
The main thing to remember with lights intended for cloning is that they have to be cool. The typical high-temperature, high-output lights used for vegetative and flowering growth are far too harsh and hot for cuttings undergoing the rooting process.
Thus, use cold fluorescent (CFL) or light-emitting diode (LED) lamps, and be sure to choose blue-white (“cool white”) light. In springtime when plants naturally grow, the daylight is shifted more towards the blue end of the spectrum. In late summer and autumn, daylight shifts more towards the red end of the spectrum. This is why lights intended for the flowering period are more yellowish-red and vegetative lights are bluer. For clones, stimulating vegetative growth (i.e. growth of leaves, stems and roots) is obviously of the utmost importance.
Trays, tools and cloning kits
Specially-designed cloning trays are available from most garden stores, and are useful as they provide individual spaces for your cuttings to occupy. This helps to prevent roots of different plants from becoming tangled as they grow.
There are also various complete hydroponic and aeroponic clone set-ups available, which comprise lights, trays, ventilation and irrigation all in one. Ready-made set-ups can be quite pricey, but it is possible to build one’s own for significantly less.
However, it is also possible to simply use cheap plastic trays or boxes without allotted spaces for each cutting. If the roots do become tangled, it won’t harm your cuttings if they have to be cut. In fact, some growers believe that this harsh treatment encourages fresh root growth with more abundant branching.
Preparing your cuttings
You will need:
- A mother plant;
- Scissors or secateurs; a sharp, clean razor blade or scalpel;
- A cutting surface such as a silicone baking sheet or ceramic dish;
- A cup or glass 2/3 full of lukewarm water;
- A growing medium such as rockwool cubes;
- Rooting gel or powder; a plastic spray mister bottle;
- A (preferably heated) propagation chamber.
Method for taking cuttings/cloning cannabis
- First, soak your rooting blocks in water thoroughly, for up to fifteen minutes to ensure that they are saturated. Adjusting the pH of the water to around 6.0-6.5 prior to soaking the cubes is advisable.
- While the medium is soaking, use scissors or secateurs to take cuttings from the mother plant. Cuttings should consist of the outer 3-4 leaf nodes of a terminal stem or branch.
- Using the razor blade or scalpel, trim all but the topmost leaf nodes off the cutting, as close to the stem as possible.
- Cut the stem at a 45° angle. Some growers use the blade to scrape away the outer layers of bark and expose the inner stem from which new roots grow; others believe this step is unnecessary.
- Dip the cutting into rooting hormone, making sure to thoroughly coat the bottom 1cm or so of the stem.
- Remove the rooting blocks from the water and lightly squeeze out some water so that they remain wet but not dripping.
- Insert the hormone-covered stem tip into the rooting block to a depth of 3-4 cm. Place the cutting into the propagator.
- If correct conditions are maintained, in 2-3 weeks cuttings should all have visible roots protruding from the rooting blocks and be ready to transplant.
Maintaining cannabis cuttings
As a general rule, your cuttings should be kept at a constant temperature between 20°C and 26°C, and at a relative humidity of 90-100%. The relative humidity (RH) can be reduced somewhat after the first two or three days, but should never drop below 60-70%.
Cannabis requires specific conditions to be maintained if cloning is to be a success. Furthermore, the three main subtypes of cannabis, informally known as “sativa”, “indica”, and “ruderalis”, can vary to some extent in their requirements.
As most commercial strains are now heavily hybridised and their genetic lineage unclear, trial and error may be the best way to ascertain the individual requirements of a specific variety. Be prepared to lose clones, and until you are certain of a strain’s requirements, take more clones than you anticipate needing.
Humidity, temperature & mould
Cannabis is prone to rot and mould, particularly powdery mildew and botrytis (grey mould). Great care must therefore be taken to prevent mould while maintaining high enough moisture levels for plant tissues to remain adequately hydrated and rooting to occur.
Prolonged direct contact with water itself (such as in an overly-moist growing medium) will also cause stems to decompose. Stem rot taking hold, whether through a fungal agent like botrytis or through direct action of water, will usually result in clones needing to be thrown away.
However, maintaining a consistently high humidity and a consistently low-to-moderate temperature also provides ideal conditions for mould growth. Maintaining good airflow (usually a small fan will suffice) helps to combat this problem, by carrying saturated air away and bringing fresh clean air to the fragile stems and leaves.
If you are about to clone some of your cannabis plants, then we assume you’re an advanced grower. But that doesn’t mean that ventilation isn’t worth mentioning in this article because it’s extremely important for the health of your clones. Here are a few things to think about:
- Clones are just like tiny seedlings. They are fragile. Excessive humidity creates the perfect conditions for airborne pests such as fungus and mould. Ventilation can keep the humidity at a good level for clone rooms.
- “In-flow” ventilation (HEPA filters are recommended) is more important than “out-flow” ventilation. Clones don’t produce much odour so there’s no need to filter air out of the room. However, fresh air needs to be brought into the room regularly to “recycle” the air, keep it clean and maintain relative humidity.
- Even though your clones are in covered trays, they need to breathe! It is important to open the tray for a couple of minutes every day to give the air inside the tray a chance to refresh. This is also a chance to inspect them for early signs of diseases or pests.
Successfully cloning cannabis plants is one of the trickiest aspects of growing cannabis for novice growers, and even with years of experience it can remain pernickety. Following the advice given above will usually bring about good results, but trial-and-error is still the best way to “get the feel” of taking cuttings.
- Disclaimer:Laws and regulations regarding cannabis cultivation differ from country to country. Sensi Seeds therefore strongly advises you to check your local laws and regulations. Do not act in conflict with the law.