So, two specimen plants went on the block, selected for not being not particularly dramatic or attractive. Both were about 7 months old, grown from Mark Dimmit seeds. They are both A. arabicum x crispum, quite vigorous.
To start, dig them out of their pots and wash the potting medium off the roots. You want to examine how the tap roots are developing and decide whether you want to keep them or not. The first one I picked, for instance, turned out to be the one I had previous experimented with by twisting the roots together. When I dug it out, it looked like this:
Now, that is a nice twist! I want that twist. Ergo, it went back into the pot; this time labeled so I will not accidentally dig it out yet again for future experiments. I picked another plant--it had nice branching and was about to go dormant so I did not initially want to touch it. But it turned out to have a boring tangle of roots underneath the soil so that one went into the project instead.
I don't like touching my camera with adenium sap all over my hands so I have no photo of the sliced pieces but there is really nothing mysterious about this step.
Before making the cuts on the two pieces, make sure you have prepared the following:
1. Pre-cut pieces of transparent packing tape, just enough to tape around the two pieces with about an inch of overlap. You will probably need at least two, depending on how complex the shape of the plants are. I needed two to hold them together at the proper angle.
3. Box cutter or a pair of scissors, whichever one you are most comfortable with using with one hand. I am partial to box cutters.
4. Cutting surface. Corrugated cardboard is the best---thick enough to catch the sap yet with enough yield to support the side of the plant.
An important thing to remember before cutting the plants is this: you want to make sure that the exposed surfaces will fit each other snugly at whatever angle you plan to join them. They do not have to perfectly match but you have to try and match the surfaces as closely as possible to make sure that there are no huge areas exposed and the entire cut surface on one will seal the cut surface on the other plant. You may want to mark the spots with crayons. I am pretty good with eyeballing these things so I did not have to. I'm just saying.
Use a sharp chef's knife---a smaller knife will force you to wiggle the cut. It is better to make one clean chop once you have decided what portion to cut.
Double check your tapes and what not. Go pee or whatever. Once you have sliced the plants, you have to work fast before the sap dries out completely. So again, keep rotating the plants, examine the fat roots, look at the branches---you may have to prune them as I ended up doing. When you have committed to how you are going to slice these mothers, just hack away.
I know people keep saying clean the knife with alcohol before cutting another plant that you will graft or conjoin. But think about it. These two are going to be sucking faces. That's as direct an exchange of infestation as physically possible. So don't bother interrupting the surgery by spritzing alcohol in between cuts. What is more important is to be able to make a clean, flat cut. Unless the cuts on both plants are flat, the two pieces will rock back and forth against each other when you stick them together. This instability will prevent the plants from healing together as fast as possible.
Adeniums on This Desk: Unite!
So once you have hacked both plants, press the exposed surfaces together in the angle you want. If you want to rotate, try to do it without disengaging. However, if you think you got the slice wrong, then just slice again.
Then, once you got the angle right, carefully tape the two plants together like so:
Because of the shape of these two plants, I had to tape them together at their widest first, then put another tape above that to ensure a firm grip.
Now note where the color changes between the top part of the plants and the bottom parts that were previously under the soil. Since the cuts on both plants are going to be partially exposed above the soil, put another tape to protect that exposed fissure. What you want is to be able to water this without getting that fissure wet.
If the joint is wobbly, or needs to be pressed more firmly together, you can use a rubberband. But make sure there is only enough pressure to hold the two plants together but not so much that they are squeezed against each other. In SCUBA terms, you only want it "finger tight". Once the plant is watered and has recovered enough from this surprise, it will rehydrate and even start expanding. If the rubberband is too tight, it will scar or even potentially strangle it.
When you are satisfied that the joint is stable, you can pot it up. This pair is going to be extremely moisture-sensitive so your best bet is planting it back in a 5-1-1 mix (five parts bark, one part pumice and one part granite). This proportion will store enough moisture without soaking the healing pair too much for too long. Bury the pair up to the soil line of the bigger plant, if they are of unequal size.
From here on, you will be watering this pair around the rim of the pot, away from the base of the plant. You want to get the potting medium wet, not the plant itself. Keep it warm and in the shade. I did this project in winter so it was on top of a plant heating mat and under T5HOs which is enough heat and light to help it along. If you do this in summer, keep it in bright shade until you see that exposed fissure visibly heal.
Don't Like How It Looks? Rip it!
I'm only adding this portion just to demonstrate that having to redo this whole shit is not necessarily an irreversible disaster. Yeah, sure some Übermensch will get it right the first time but even if you did and you just happened to change your mind about the way the conjoined pair looks, you have, at most, three days to change your mind. Beyond that, healing would have started and it will just be rude to go in there and start hacking again. Rude. But not impossible. Even then you can still go back. The longer you wait though, the higher the risk of just pissing the things off.
My first attempt with these two plants, for example, looked like this:
It looked wimpy even though the cut is actually more drastic under the soil. After a few days of rumination, I ended up digging it out and starting over with fresh cuts that were slightly more radical; ultimately settling on as much cut as could be done without compromising the large well-shaped taproots underneath that I meant to keep. Ultimately, this is what the conjoined pair looked like:
As expected, part of the process was having to prune a number of branches from both plants so that they do not tangle too much as they grow back leaves of possibly develop more branches down the road.
This experiment was done in November and by April, the joint has sealed. This process will probably take less time if done in high summer. In this case, the tape and rubberbands were removed in March. I probably could have removed them as early as January, from the looks. I just never got around to it earlier.
That's it, yo. Space-saver.