Impact of Liner Planting Practices on the Finished "Package"
The majority of landscape trees purchased from local nurseries in Illinois, and the Midwest, are planted as liners. Quality of the liner stock is important, and so are the planting procedures. If not planted correctly, high quality liners can become poor quality landscape trees.
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Description of Structural Roots
The structural roots are the large woody roots giving characteristic form and shape to the root system and form the root flare. Typically they are not far below the soil surface. “First order lateral roots” is another term that has been used for these roots.
The structural roots begin to form very early. On seedlings, they start as the natural lateral roots arising from the primary root just below the soil surface. On cutting and tissue culture propagated plants, it is the adventitious roots formed very early that usually develop into the structural roots. Often they are formed only at the bottom end of the cutting.
The uppermost structural roots will eventually form the root flare and so they should radiate out in all directions.
Proper Planting Depth
Natural lateral roots (structural roots) of seedlings are often replaced by adventitious structural roots regenerated from the cut end of the primary root after it is pruned during field nursery production. These adventitious structural roots have been referred to as the adventitious root flare (ATF). The area of root between the ATF and natural transition to stem tissue has been called the root shank. A root shank longer than a few inches will lead to deep planting if the natural depth is maintained. On some species, additional adventitious roots may be produced on the root shank after planting, but this is not common.
Planting high to compensate for a long root shank will raise the bud union higher above ground, which may be aesthetically undesirable. Sudden exposure of this root shank tissue to above-ground environment it is not accustomed to, could result in cold or sun injury in some species. When planting high, it may be best to cover the root shank with a mound of soil that can erode away gradually.
Location of Bud Union
The bud union and/or cutoff wound should be seen above ground at the base of the trunk, at same depth as when it was grafted. This is typically about 1-2 inches above the soil. The presence of this bud union or cutoff is a sign that the liner was planted correctly, not an indication of inferior quality.
In-Ground Planting Methods
Depending on the size of the liners, and the preferences of the nursery manager, field-grown and container-grown liners may be planted by machine or by hand. Trenches or holes are often dug by machine for hand planting.
Regardless of planting method, the roots should be located at the proper depth (Proper Planting Depth) and spread evenly in all directions. Avoid creating circling, twisted, or “J” roots by dragging or twisting the liner while planting. Pulling the liner up to adjust height after backfilling can also distort the root system and force the roots into the vertical position.
