Anyway, I've developed my own method that works for my own location and for most of the trees that I plant. So far the only tree that I've continually failed with is cacao. I don't know if it's my planting method (and I've tried different ways), the location the trees were planted, or some other reason. But to date I haven't managed to keep a cacao tree alive for more than a few months.
#1- I pick a location that the species prefers. Sun? Semi shade? Shade? I also consider the soil moisture situation. For example, avocados don't like wet feet nor do they like shallow roots. Other trees aren't that fussy.
-#2- If the spot has grass growing there, I'll strip off the sod, setting it aside to use later. It will go back into the hole as fill material.
#3- Dig the hole. Around here it isn't as simple as it sounds. A shovel usually isn't enough, so I use an o-o bar to remove the lava rocks. When I can, I will make the hole 18" deep, but I hope for 24". If I can only get down 10-12" then I move to a different spot.
#4- I'll separate the soil be small rocks from the big lava chunks. The soil and small rocks will be going back into the hole.
#5- In the very bottom of the hole I will put some sort of future plant food for the tree. Perhaps manure that might have dangerous pathogens such as dig poo, catbox cleanings, pig manure, human manure. While I don't routinely use human manure, I know of people who do. Under a tree is a good spot for it. Also small dead animals will do, such as roadkill birds & mongoose, etc. As I add this material into the hole I layer it with the soil, sod, and small rocks I had previously removed while digging the hole. I will also mix in a small handful of wood ash and a hefty handful of burnt crushed bone. I fill the hole to 10"-12" from the top.
#6- Stomp the fill material down and add a gallon of water. Wait at least two weeks.
#7- Stomp the fill material down again. Feel the surface of the fill material. If it is cool, then go to step 8. If it is warm, add one gallon of water and wait another week. Any warmth from the fill material composting will damage or kill a young tree that is planted atop it. Heat is more common if small animals were used.
#8- Now I'll plant the tree. Soil and small rocks are used as needed to fill the hole. I'll immediately water the young tree well, then check it weekly for soil moisture, diseases, and pests.
Just about all my young trees transplant fine this way. The reason I put a nutrient plug under the young tree is that our tropical soil is not very fertile. That nutrient plug seems to help the tree while it is establishing its lateral root network.
I'm told that this method isn't necessary. And perhaps in many regions that's the case. But I think it's ok for here and it's a way to utilize material I don't want in my veggie garden, the various manures and decaying small animals. No waste.