A new grafting methodology for medicinal cannabis has been developed which may increase biomass yields without adding any time to the cultivation process. In a study carried out by Dr. Sarah Purdy of the New South Wales Department of Primary Industries and her colleagues, grafting high-yielding plants to strong rootstock not only produced higher-yielding plants, but also changed some of the composition of cannabinoids produced by the plants.
Grafting is a technique that has been used to improve crops for hundreds of years, and has been successfully implemented to improve crop yields of plants such as watermelon, tomatoes, and capsicum. The practice of grafting involves cultivating rootstock and then grafting the part of the plant to be harvested, called the scion. In this experiment, two plants with strong root growth were chosen as rootstock. These rootstock plants had a relatively low flowering biomass, and so high-yielding plants were chosen as scions. Several different high-THC producing plants were selected to be the scions.
One of the grafted scions in the experiment resulted in greater root mass for two different rootstocks. An issue commonly present in many high-THC producing plants is the variability in root biomass. In a commercial setting, plants with low root mass may provide acceptable yields but may require more maintenance during the growth process. This new technique may provide a solution to this inconsistent root performance in plants with desirable flowering traits; by grafting to a rootstock with greater root biomass growers can improve the overall performance of these plants.
Some of the grafted plants resulted in higher concentrations of certain cannabinoids compared to non-grafted plants. For example, in one of the grafts involving a high-THC rootstock with a high-CBD scion, the concentration of CBDA increased to 8.6% from 7.6% in non-grafted plants. One of the high-THC scions also had a tendency to increase in THCA content. The researchers note that overall, cannabinoid content did not change much from the process. These slight changes do hint at possible research avenues related to plant development and chemical signaling.
Researchers believe this new grafting process will have benefits in cannabis research. Other grafting methods have been used to identify genes and hormones that are important in the plants’ communication systems. For example, strigolactones, hormones which are derived from the root system of plants, can cause a phenotype with increased branching. The differences in branching seen in the experiment may be a result of the interaction of strigolactones from rootstock with the grafted scions.
As cannabis cultivation continues to become more widespread, coming up with sustainable practices for increasing yields is important in both the commercial and home setting. We may not see this technique become widespread in a commercial setting, but it is definitely interesting information for the home grower who may want to try this technique to increase yields. It is also great to see that cannabis research is being taken seriously, especially considering the economic and medicinal value of the crop.
One-step Method for Grafting Cannabis
Things You’ll Need
- 70 or 80% alcohol, either isopropyl or ethanol, in a spray bottle
- Clean water in a spray bottle
- Clean tissue
- Cutting board
- Clonex gel in a small container
- Grafting clips
- Propagation medium in container (e.g. coco-peat or rockwool trays)
- Propagation dome
- Temperature and humidity monitor
- Clean all equipment by spraying with alcohol
- Soak the propagation medium with water
- Cut a ~20 cm stem from the top of a mother plant to provide the rootstock (A).
- Remove all leaves from up the side of the stem with secateurs.
- Excise the leaf bunch at the top with a scalpel and then cut the base of the stem diagonally across a node with a scalpel. The stem piece should be approximately 10 cm long.
- Make a 1 cm vertical cut down the top of the stem for the scion to connect to (C).
- Gently scrape the bottom 1 cm of the rootstock stem with a scalpel (this will aid root development).
- Cut a ~20 cm top of a mother plant to provide the scion (D).
- Cut all the leaves from the sides of the stem with secateurs, leaving the leaf bunch at the top.
- Trim the leaf bunch to the length of the shortest leaf with secateurs (E&F)
- Cut the stem to result in a total scion length of 10 cm with a scalpel (F).
- Gently shave two opposite sides of the bottom 1 cm section of the scion into a pencil shape with a scalpel (G).
- Wipe the union zone of the rootstock and scion with a tissue soaked in alcohol.
- Slide the scion into the cut made in the rootstock stem and secure with a grafting clip.
- Dip the bottom of the rootstock stem into the clonex gel and place it into the propagation medium.
- Place the graft inside a propagation dome. If using a tray of propagation plugs, complete the tray as quickly as possible and then place the tray of grafts into the dome.
- Spray some water inside the dome, and place a humidity and temperature sensor inside and close all vents.
- Keep the clones under a PAR of 100-150 µmol m-2 s-1 and temperature of 25 degrees Celsius (77 F). Retain 100% humidity for 7 days and then progressively lower it by opening the vents and then sliding the lid away from the base over the remaining 7 days (see table for target humidity).
- The plants will wilt significantly in the 24 hours post grafting. This does not mean they have failed (J).
- The plants will regain turgor 48 to 72 hours post grafting (K).
1 – 7 100
11 – 14 80
“A One-Step Grafting Methodology Can Adjust Stem Morphology and Increase THCA Yield in Medicinal Cannabis,” first published in Agronomy, March 2022.