I know this is old, but after reading the comments I had to interject. Treat it just like you would a wound on a human...

Step 1: Assess the damage without touching, and probably causing further damage. Determine weather you want to attempt to repair the plant, reroot the severed piece for planting later while trying to nurse the original until the wound heals, or say "Adios" by asking yourself a few questions. What happened? What caused this to happen? Where is the primary damage located? is there secondary damage? With my help can this plant heal or is it a total loss (you'd be surprised what plants can survive!)? Is it worth saving or do I have tons of this plants and the time spent caring for it will be better spent caring for the other plants?

Try to save it because you love that plant, it was fruit laden and you can't bear to lose all that delicious fruit of your hard work, and/or you just want to know how & that you can?! Great!

Step 2: clean and sterilize the wound and any thing you will use in this plants repair or face the very likely possibility that the plant you're about to work so hard to save will look like it's getting better (because it will be due to your quick action in saving it) until the disease/virus it contracted via the open wound that was exposed to the soil and air for however long didn't get cleaned and sterilized when you used your grubby garden fingers to perform plant surgery and then used an old mildewy roll of duct tape you found in a cardboard box on the side of your house...

It could be totally fine, too. I just know I would prefer my surgeon to use sterile tools when reattaching me when I split open.

Step 3: Visualize what needs to be done in order to not injur the plant again or to cause the damage to get worse or split further. sometimes if it's a vertical split down the length of the plants main stem I'll use some large gauge natural fiber twine (⅛" jute) to wrap snuggly around the stem below the split until I've come just past where the split starts and then tie it off or secure so that the knot or securing is easily undone when you're ready to splint. This way it protects the split from growing or getting worse as you start to handle the plant.

Step 4: Get everything you need to make the repair. This is kind of up to you because every repair will be different. A splint is likely what you'll need to make but not always and size will vary according to your plant and scale of the injury. You can make splints out of tons of things lying around the house. firm backing for the splint pieces and something to hold them together on either side of the split is all there is to it. This could be popsicle sticks and tape or bamboo garden stakes and rope/bungee cords. I've even used routed out 2x4's and C clamps to fix a badly damaged fig tree grown from my father's ashes.

You'll also likely need support to take tension off of the pieces that split so that they can properly heal. if you don't do this then it will never heal correctly or take too long to heal causing the rest of the plant to suffer because it's putting all of its energy into healing this wound that pulls open a little with ever passing breeze.

Step 5: With adequate support in place or within arms reach, carefully right the plant so that the two halves or the split are in line with each other and in the position the plant will remain in during it's healing and growth. Once achieved temporarily support the plant in this position with a cage & ties, several stakes & clips, or even with twine from an over head boom like a nearby trellis or a sturdy structure you can anchor the plant to from above to hold it in place while you work.

Step 6: if time has passed or you might have contaminated the wound, you can clean again now that it's been moved around and possibly opened further. I use lukewarm h²O, Dr Bronners Original Castille (dark blue label & smells like peppermint), and h²O² (Hydrogen Peroxide 3%) at a ratio of

USE AT OWN RISK! ALWAYS TEST NEW DIY SPRAYS BEFORE MASS USE!

1T Doc Bronners

8T h²O² (Hydrogen Peroxide)

1 gal h²O (distilled)

If you don't want to use this or can't because it's a sensitive plant species then just take some clean water and spray the wound to help flush the site from debris or surface disease.

Step 7: Bring the split in line together and splint, making sure to try and fit the break back together like a puzzle. the closer the match the easier and faster the heal. Once the splint is in place snuggly wrap with clean dry paper towel or piece of cloth (Ace bandage works well too). Secure the wrapping and splint with tape or twine or any other means.

Step 8: Reposition or make more permanent your support system. ensuring that the plant is fully supported with no weight or tension on the injury point OR any other weak points that the weight distribution and new support contact points may have created.

Step 9 (optional): I do this sometimes but not Everytime. If the plant was injured due to some kind of environmental or nutritional stressor (too hot, too wet, nutrient sufficiency etc.) I try to give the plant a little boost regarding that issue. a drink of water (not too much) & some food to fuel it for it's recovery. Not too much because it can shock it or cause further issues. I usually use some liquid fish emulsion & water to feed and water at the same time. I also sprinkle pure ground cinnamon over the wound & wound area after the repair plus around the base of the plant and soil below the plants canopy. Cinnamon has antifungal properties and is also used as a rooting hormone. it keeps the site dry and free from fungus and disease spread, pests generally tend to steer clear of it and it seemingly helps the plant regenerate it's cells more quickly (unproven but it works for me).

This is my best advice. It comes from a person who feels the internet lacks truth, substance, detail, and alternative options that explain why they do it that way. I've also had lots of success doing it this way. You may or may not too.