The term “cloning” is simply another, easier way to say vegetative propagation. Using this process, each cutting is a genetic copy of the donating plant. The small branch continues to grow even after it is separated from the original plant, effectively allowing the same plant to be grown in separate containers. This allows the plant to have an extended lifetime, even beyond the demise of the original.
The selection of a superior mother plant is an important step as its traits are perpetuated by its clones. So, make sure that it is desirous to make many copies of that same plant. Generally, the most desirable attribute in a cannabis plant is being of the female gender. Cannabis plants grown from normal (not feminized) seeds tend to be about evenly split between the sexes. This means a grower needs to start at least twice as many seeds to achieve the desired number of female plants since losses to male plants will be about half (depending on sample size and luck). Cuttings taken from a known female plant, however, produce only female plants, meaning the culling of males is not required. A single known female can be the mother plant to tens, hundreds, or in extreme cases, even thousands of genetic copies of itself.
It is possible to root cuttings because of meristem cells. No matter where they are in the plant, all meristem cells are the same basic building block cells. These cells are undifferentiated and have the potential to mature into a wide variety of different cells, such as leaf, root, flower, etc. In cloning, the stem of the cutting is kept moist, oxygenated, and alive until the meristem cells near the surface decide to develop into root cells instead of the branch cells they otherwise would have become.
Rooting Cannabis Cuttings
Cannabis cuttings root easily and well, which is fortunate for gardeners and growers. Before taking the cuttings, a space for the clones should be prepared. The space should be tolerant of spills (which can easily happen) and have moderate lighting as the cuttings will be tender until they are established. Common options include T5s and LEDs, and some growers place the clones along the edge of an HID garden space. Comfortable to warm room temperatures are also desired, although a specialized heating mat can be used to raise temperatures if needed. If a heating mat is used, one with a thermostat is recommended to prevent overheating. As with any electrical equipment with cords in the garden, make sure there is a “drip loop” in the cord so any condensation drips off the cord instead of running into an electrical socket.
Once the space for the clones is prepared and a mother plant chosen, the cuttings can be taken. Cutting should generally be taken from plants still in growth. While taking cuttings in flower is possible, they take much longer to root. Cuttings should include at least both a shoot apical meristem (growth tip) and a section of the stem. In situations where the cuttings will be crowded together, it is common to trim large leaves to ensure one plant doesn’t shade another.
Since the cuttings have been separated from the root system of the mother plant, they must have access to moisture until they develop their own roots. Fresh cuttings are particularly sensitive to drying out, leading to terminal wilt, so they need a lot of moisture to survive. However, they must not be kept too wet as fungal problems such as damping off, molds, and root rot can kill clones as assuredly as dehydration can.
A common practice is to immediately place the end of each cutting into a container of water. That way it won’t dry out while the remaining cuttings are taken. Once all the cuttings are made, however, they need to be moved to another medium. To keep the ends of the stems wet, there are two basic methods: either put the stems in something that retains moisture or continuously expose them to a mixture of water and air. In the first case, rooting cubes, vegetable pods, or small pots are popular options. Rooting cubes can be made from a variety of materials, and they should be moistened before the stem is driven (gently) into their centers. Vegetable pods have depressions that can be filled with potting mix, and small pots or cups can be used similarly. Standard 10x20-inch 1020 trays are commonly used to hold these clone containers. These are sold in single- or double-thickness options, with the double-thickness trays being noticeably sturdier. There are plastic domes that fit over 1020 trays to help keep the humidity higher in dry climates, but they should be used with care and moderation as clones in overly wet conditions are prone to damping off and other pathogenic fungal growth.
To instead expose the cutting ends to a mixture of air and water without a growth medium, the cuttings are suspended above a chamber containing the water and air mixture until roots develop. Air pumps can be used as the driving force to either run an air stone bubbling in water or an airlift sprayer. In some configurations, a water pump may be substituted for the air pump, but they should be used with caution as they tend to transfer more heat to the water.
The Bottom Line
Regardless of the specifics of the method used, the goal remains to keep the cuttings alive and healthy until roots develop so they can be transplanted into a larger container for further growth. A mild nutrient solution may be introduced once roots have appeared, but overfeeding tends to be a more common issue than underfeeding, so mix lightly and save most additives for later. Also, though not required for success, hormone auxins such as idolebutyric acid (IBA) or naphthaleneacetic acid (NAA) can be used to encourage the meristem cells to become root cells instead of leaf cells. They are commonly found in rooting powders, liquids, and gels, and are coated on the cut ends of the stems.
Cloning is not a difficult skill to acquire, and it is recommended for any grower that would like to take advantage of the ability to replicate specific cannabis plants. It is a technique that can be used to determine the sex of a plant or to create multiples of a known good female plant. A single rooted clone can then be turned into a roomful of copied plants that should grow similar to each other in similar conditions. Even if cloning isn’t an activity that appeals to a grower, it still behooves them to understand the nature of clones and their abilities.