Cloning cannabis is a method of propagation that allows growers to create genetically identical copies of a desirable mother plant. This process ensures the resulting plants, known as clones, retain the exact traits—such as growth structure, potency, and yield—of the parent. Rockwool cubes are a popular inert medium because their fibrous structure holds moisture exceptionally well while also providing the necessary air pockets for oxygen exchange at the root zone. The cubes are clean and sterile, minimizing the risk of introducing pathogens. Success in this technique relies on precise environmental control and careful handling.
Preparing the Rockwool and Cloning Environment
Preparing the rockwool cubes is the first step, as untreated rockwool has a naturally high pH that can inhibit nutrient uptake in cannabis. The cubes must be soaked in water with a pH adjusted to a range of 5.5 to 6.0 for several hours to stabilize the medium. Achieving this slightly acidic range ensures the future roots can efficiently absorb micronutrients. After soaking, the excess water should be allowed to drain off, leaving the cubes moist but not waterlogged, which prevents potential stem rot and root suffocation.
The entire cloning area, including tools and surfaces, must be sterilized to prevent the introduction of bacterial or fungal pathogens. A sharp razor blade or scalpel is preferred for making the cuts, as dull tools can crush the stem and increase the risk of infection. A dedicated cloning tray should be set up, often with a clear humidity dome placed over it to create a sealed microclimate. If the ambient room temperature is low, a heating mat placed beneath the tray can help maintain the ideal root zone temperature of 72–78°F.
Taking and Processing the Cuttings
Selecting the correct material from the mother plant is vital for clone success. The best cuttings come from healthy, non-flowering branches that are sturdy and have two to three nodes. Taking cuttings from the lower sections of the plant is often recommended because these areas naturally contain higher concentrations of rooting hormones. The cut itself must be performed swiftly using the sterilized blade, making a single, clean slice at a 45-degree angle just below a node. This angle dramatically increases the surface area from which new roots can emerge.
Immediately after the cut is made, the stem must be submerged in water to prevent an air embolism, where an air bubble blocks water flow and causes the cutting to wilt. While submerged, trim away any large fan leaves and the lower growth nodes that would be below the rockwool surface to reduce water loss through transpiration. Some growers also lightly scrape the exterior layer of the stem base with a clean blade to expose more cambium tissue, further encouraging root initiation.
The prepared cutting is then ready to be dipped into a rooting hormone, typically a gel or powder, which contains auxins that promote root development and simultaneously seals the wound. Once coated, the cutting is carefully inserted into the pre-soaked rockwool cube, ensuring the hormone-coated tip is not rubbed off during insertion. The cutting should be firmly seated upright in the rockwool.
Maintaining Conditions During the Rooting Phase
Once the cuttings are in the rockwool, maintaining a stable and appropriate environment under the humidity dome is the main focus until roots appear. The dome must remain closed initially to trap moisture and maintain a relative humidity (RH) between 70–80%. This is necessary because the unrooted cuttings cannot yet draw water efficiently through their stems. Consistent air temperature in the 72–78°F range should be monitored, as temperatures outside this window can slow or prevent rooting. Low-intensity light, such as fluorescent or low-wattage LED fixtures, is sufficient and prevents the clones from becoming stressed.
A light cycle of 18 hours on and 6 hours off, or even 24 hours of continuous light, is typically used to ensure the cuttings remain in the vegetative growth phase. After the first few days, begin “burping” the dome, which involves briefly opening the dome once or twice daily to exchange the air and prevent mold or mildew. This gradual exposure to fresh air is the first step in hardening off the clones, slowly preparing them for a lower ambient humidity.
The rockwool cubes should be kept consistently moist but never saturated, which can be achieved by misting the inside of the dome or the cubes themselves. Roots typically become visible protruding from the bottom of the rockwool cubes within 7 to 14 days, signaling successful rooting.