Hi rezo,
From the little I know of grafting, it's always done above the crown (where the stem meets the soil) of the host plant to which cuttings are grafted unto.
True grafting would be where a single cannabis plant is used that has been in veg for some period of time and pinched back to produce several stems. Next the healthy stems would be cut at an appropriate point (not sure where the best place would be, near a node?) and cuttings taken from other strains would then be joined (grafted) to the cut stems and supported until the graft took. If successful, the outer layers would grow together and become one outer layer or one skin, so to speak. Water and nutes would come up from the roots of the original plant would make their way up the main trunk of the original plant and flow to the original plant's separate stems into the stems of the grafted cuttings. Sound like a lot of work for cannabis plant but may be possible. This is the technique used for grafting of the apple and cactus plants mentioned. If one was successful at this, the resulting plant with it's grafts could be used as a mother plant with cuttings taken from each of the grafted stains (Cool!).
What you're trying to achieve would be happening below the crown of several plants (cuttings), below the soil line. At best you would have several cutting succeed in growing with each developing its own root mass and each still having its own stem. These would compete for available nutrients, light and air once they go into the veg period. This would be like planting several seeds in one hole and all of them germinating with no subsequent thinning being done. Either way, cuttings or seeds, several plants would be crowded into a single hole resulting in both root, stem and leaf congestion and would produce unhealthy plants in the process.
An unwanted mother plant would be a good candidate for grafting cuttings unto but you would want to read up on grafting before attempting to do so. I believe grafts are wrapped or covered with hot wax (?) or other substances while waiting for a graft to take to ward off the possibility of infection and/or bug infestation.
I hope you have some measure of success though if you've already begun your attempt but if not then I'd recommend going with the "above the crown method" if you try anything at all. Good luck!!!
