In cannabis cultivation, cloning is one of the best ways to maintain strain variety and genetics, and it has also been widely used by commercial and professional growers. But it is not as so simple of sticking the cuttings into peat pellets as it seems to be. To produce successful cannabis cuttings with a well-developed root system in a short period of time requires careful management of the environment, especially air and media temperature, humidity and light. Misting or fogging should be managed, based partly on the light intensity, to ensure leaf surfaces don’t dry before roots are established, and then the frequency should be decreased as the root system develops.
Light and temperature primarily drive the rate of root development. Managing light is at least as important because inadequate light delays rooting while too much light can excessively increase leaf temperature and cause plant stress. Managing light in a greenhouse is also more challenging because solar radiation is always changing. So Many growers improve the rooting of cuttings by more closely managing light during propagation, and the most efficient lighting system has shifted from fluorescent to current LED grow lights.
Manage the PPFD level in different phases.
Light provides the energy for callus formation and the subsequent generation of adventitious roots. At the same time, light increases plant temperature and accelerates the drying of leaves, which can quickly dehydrate cuttings. (under LEDs, this would be less of an issue.) therefore, the instantaneous light intensity during the early rooting phase should be quite low (but not dark) and then increased as roots develop. Managing instantaneous light levels is especially important during the first week of propagation because of the vulnerability of unrooted cuttings, and also because this first week strongly influences the ultimate success of producing high-quality liners.
A suggested maximum light intensity is between 100 to 150 μmol∙m−2∙s−1 from the time cuttings are stuck until the initial roots form (a few millimeters in length), which is usually the first five to seven days of propagation. The frequency of misting or fogging should be adjusted based on the light levels, with greater frequency under higher light and vice-versa. Identifying this mist/light relationship can greatly improve rooting.
Once roots have begun to form, the light intensity can be increased to a maximum of 200 to 300 μmol∙m−2∙s−1 for the next four to seven days as the roots develop. Cannabis cuttings can tolerate even more light when half of each liner cell is rooted, approximately 10 to 14 days after stick. When other factors are closely managed, most cannabis cuttings can be well rooted within three weeks.
Pay attention to daily light integral (DLI).
During propagation, the light should be primarily managed based on the instantaneous intensity, but the DLI should also be considered. Research at Michigan State and Purdue universities has shown that the rooting of many crops is delayed when the DLI is less than about 4 or 5 mol∙m−2∙d−1. Therefore, monitor the DLI to ensure crops are receiving enough light on a cumulative basis.
Light uniformity is vital for uniform high quality cuttings.
Light intensity should be as uniform as possible during propagation,a more uniform light environment both horizontally and vertically within a liner tray is essential for the uniform morphological development of the cuttings. VANQ GLTW040 series LED grow light tube has been design with a unique rectangular light distribution footprint. More importantly, due to the special reflector design, the PPFD level is much more uniform comparing to other grow light tubes on the market.Please refer to the PPFD test chart as below. This will eliminate bright “hot spots” and improve the uniformity of rooting. To determine how well light is scattered in your linear tray by yourself, use a light sensor and watch the values change as you move it through the propagation area. If the values change by more than 25 percent or so, you need to adjust the layout of your grow lights.