Preparing the Area
No matter what type of soil the tree has grown in before it arrives in your yard, it must adjust to the type of soil there. Consequently, planting techniques encourage them to do this. Remove all lawn sod from the area.
Remember, most tree roots grow outward, only 8 to 12 inches below the soil surface, rather than down into it. The best way to encourage them to venture into the new soil beyond the hole is to loosen the soil over a circular area beyond it roughly 3 times the width of the rootball. Use a hand lawn aerator, or a pitchfork to punch into the soil, then rock back and forth to loosen it. Repeat over the area. Tilling is not necessary and is likely to disturb roots from nearby plantings.
If the soil is very compacted, heavy clay or very sandy, work in some chopped leaves, peat moss or other organic material as deeply as possible in this loosened area. Tender root tips will be more inclined to penetrate this neighboring soil if it has air and nutrients. The extra time and labor required for this extensive preparation is not always necessary or practical. If you dig the hole and plant properly, most trees will manage fine if you are not able to do the complete preparation.
Establishing the Correct Hole Depth
The key to planting a tree properly is digging a hole the correct size and shape. The correct depth is critical. If a tree is planted too deeply its roots will not get enough air, and eventually it will suffocate.
Dig the hole no deeper than the height of the rootball. Locate the soil line at the base of the tree’s trunk where the roots begin to flare out and measure from this point to the bottom of the rootball. Loosen the burlap from the base of the trunk and brush away any excess soil from the top of the rootball to expose this juncture.
Containerized trees are already in soil at the correct depth, so their soil surface should align with the surrounding soil. Note: In cases where the soil is very clayey or drains poorly, plant even shallower, so the top of the rootball is three to four inches above the surrounding grade.
Do not put any loose soil, peat moss or fertilizer in the bottom of the hole. It is essential that the juncture of the trunk and root system remain at or just above the soil level. The earth at the base of the hole should remain firm and compact so the tree will not sink deeper later on.
Establishing the Correct Hole Width
It is also important to make the hole the correct width and shape to facilitate planting and to direct roots outward. As a general rule, dig the hole at least twice as wide as the container or rootball. Slope its sides so that it resembles a saucer. This allows leeway to maneuver the rootball for correct placement and to remove most of the burlap from wrapped soilballs.
Research and experience have shown that holes with vertical sides act like containers. Tree roots feel more confined and tend to grow in circles within the restricted space, eventually girdling the main stem and killing the tree. If your soil is heavy clay or very compacted, score the sloping sides of the hole with a trowel or edge of a shovel or spade. These indentations guide root penetration outward. Remove any loose soil that may fall into the hole.