Answer: In the professional planting scenario, the flat digger spade is inserted in the soil to the correct depth and the slit is pried open just slightly, the roots are inserted, the blade is removed and the hole is closed by stepping firmly on it. So there is a certain technique predominently used to enable a single person to plant a huge quantity of seedling trees in a hurry on a commercial basis.
So while there is not really a secret, there are some points to consider.In my experience the smaller size transplant better, and you really do need to make sure there is good soil to root contact at planting, and then water and mulch them to keep the soil slightly damp (not saturated) while they become established.
Also, when you plant, make sure the soil line (where it is above/below ground) is consistent and matches the orginal depth from before it was dug. Too, careful and prompt handling and quick planting are important. Do not let them dry out or sit in direct sun while you are planting -- wrap the roots in damp newspaper or shavings and shade them while out in the field.
Finally, make sure you are planting in a suitable location -- well drained soil of an appropriate texture and pH, full sun, protected from animal damage, and so on. Your local county extension should be able to help you determine if you have a suitable location and select evergreens that would have the best chance of surviving for you.
I hope this helps.
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