This is the second part of the post on grafting cacti and will look into more detail about the technical bit of actually grafting a cactus.
The one single thing about grafting that is of utmost importance is cleanliness. If you set to with a rusty old knife held in dirty fingers, you’re asking for trouble. Clean tools should be used, and they should ideally be disinfected at every turn (at least after every major operation) with rubbing alcohol or some other disinfectant that won’t leave traces. As with clean tools, it is naturally also vital that the cut surfaces are both clean and free of any rot, sickness or debris. Your working area should be clean and somewhere out of the sun and the elements.
For cutting larger plants I prefer either a sharp knife with a comfortable handle or a snap-off knife. For seedlings I think razor blades work best. Depending on what kind of plants you’re working with, some form of protection might be beneficial. When working with Pereskiopsis I like to use a sheet of aluminium foil folded several times to make a sort of finger-protection-device allowing me to hold the plants without having to suffer their devilish spines. A good pair of tweezers will often come in handy too. Rubber bands are handy when it comes to larger grafts to push the scion and stock together if the scion is of the globose kind and the stock plant isn’t too tall. It’s easy to push the scion off the stock with rubber bands so it’s important to be careful when using them. Weights of different kinds can also be used to put pressure on the scion so that it properly fuses together with the stock.
When grafting plants that have started rotting (in an attempt to save them), it is necessary to cut away all the diseased or rotting parts of the scion, even if it means cutting it so short that grafting becomes almost an act of futility. Almost all cacti are a nice and healthy green inside (the flesh of some species has a more yellowish or reddish hue), so any traces of black/brown or discoloured spots or marks visible on the cut surface means you have to continue cutting. And for each cut it is necessary to disinfect the cutting tool so as not to unwittingly spread infected material to healthy tissue. The cutting tool should be very sharp and, if possible, the cut should be made in one or two smooth motions and not in a sawing fashion. It’s also helpful if the cut is as straight as possible.
When grafting seedlings it is easiest to use a razor blade. The seedling can be held between your fingers while carefully slicing it in one motion. The top of the seedling will be sitting on the razor blade and can easily be pushed or nudged over to the surface of the stock plant. Once placed it should be gently rotated or wiggled a bit to remove any potential air bubbles trapped underneath, and care must be taken to place the scion so that it is in contact with some of the vascular bundles of the stock. No weights are usually needed to provide pressure on the seedling against the stock, as the sticky sap of the stock will be enough to keep it in place.
When grafting anything larger than seedlings or very small plants it is useful to shape the surface of the stock a little bit before grafting (see Fig 6). If areoles are left on the stock plant right by the cut surface, it can lead to shoots forming from them that might eventually push the scion off. Cutting away the outermost sides of the stock in an angular fashion to remove areoles will help the union be successful.
It’s extremely important that none of the cut surfaces dry out when grafting. If they do, a new cut has to be made. The stock should be cut first and, unless it’s a seedling graft which is very quick, to protect the cut surface either the top that was cut off should be put back in place until the scion is ready or a small slice of the stock should be cut and placed on top of the wound. Then the scion is cut and quickly placed on the stock (if a small slice of the stock was placed to protect the wound, be sure to remember to remove it). The scion should be lightly pushed down on the cut surface of the scion with the fingers and wiggled around a little bit to remove any potential air bubbles that might be trapped between scion and stock.
The scion gets its nutrients from the vascular bundles of the stock plant. It is therefore necessary that the vascular bundles of both parties are aligned such that there is an overlap. If they don’t align very well it is likely that the growth of the scion will be poor, which is why it is important that particularly the scion does not greatly outsize the stock . When grafting seedlings or plants so small that they do not cover the stock’s vascular bundles, they should be aligned so that they sit astride a section of the stock’s vascular bundles. This will allow them to receive sufficient nutrition from the stock. When grafting seedlings on thin Pereskiopsis stock this is usually nothing to worry about.
After the scion has been successfully placed on the stock, it should be weighted down (unless it’s a seedling) either with weights or e.g. with rubber bands over the scion and under the pot. Be sure not to squeeze the scion to death and, if using rubber bands, take care not to push the scion off the stock through poor placing of the rubber band (which unfortunately is all too easy to do). With smaller scions it is often a bit more tricky to use rubber bands, and some form of weights might be better. E.g. a small coin or thin sheet of glass or something similar might be placed on top of it, balanced against something else. It’s also possible to wrap cling film around the scion and stock to provide both a moist environment as well as some pressure.
Once the graft has been made the happy couple should be place out of direct sunlight and preferably in a somewhat humid area. A few days under plastic or in a propagator, or on the lower shelf of the greenhouse should suffice to seal the deal. Grafted seedlings benefit from a slightly more humid environment in the first few days to secure the union. If the graft is successful, the scion and the stock will have fused together within 1-2 weeks of grafting and growth should be visible within a few weeks (less with seedlings). At this point the pair should still be treated gingerly, as it’s only after a couple of weeks that the union is so secure that a mere bump or something similar won’t easily dislodge the scion.