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Choose a mother plant
Choosing a good mother plant is the most important starting step. You typically want to chosoe mothers that have proven to provide a high yield, rate of growth, potency, flowering time, flavour and effect. When growing plants from seed though, you will not know what a potential mother will turn out like without flowering it, so 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.
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 heated propagation chamber.
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 & mold
Cannabis is prone to rot and mold, particularly powdery mildew and botrytis (grey mold). Great care must, therefore, be taken to prevent mold 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 mold 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.
Successfully cloning cannabis plants is one of the trickiest aspects of growing cannabis for novice growers, but can remain challenging even with plenty of experience.