Planting Depth in Containers Affects Root Form and Tree Quality

Abstract

After 40 months in air root pruning containers, Quercus virginiana ‘SDLN’ Cathedral Oak® live oak planted 3.8 and 8.9 cm (1.5 and 3.5 in) deep from rooted cuttings had greater caliper than trees planted at 1.3 cm (0.5 in) below substrate surface. Trees in the 1.3 cm (0.5 in) deep treatment grew taller than all other trees except for those in the 3.8 cm (1.5 in) deep treatment. Most (80%) trees were graded as culls according to root evaluations in the Florida Grades and Standards for Nursery Stock. This resulted mostly from roots circling and crossing the top of the root ball in the #3 and/or #15 container sizes. Trees planted 6.4 cm (2.5 in) deep in #3s, then 6.4 cm deep in #15s, and 6.4 cm deep in #45s [19 cm (7.5 in) total depth] had fewer, smaller diameter, and deeper primary roots than trees planted at all other depths. The presence of a trunk flare and surface roots decreased with increasing planting depth indicating that these could be used as an indicator of primary root depth. Cathedral Oak® demonstrated the capacity to generate new roots above the primary flare roots only when rooted cuttings were planted into #3 containers. Trees adjusted their root systems by generating a new set of roots along the buried stem up to the substrate surface. Roots did not grow from the buried portion of the stem when trees in #3 containers were planted 6.4 cm (2.5 in) deep into #15 containers. In other words 75% or more of the primary structural roots were deflected by either the #3 or #15 container wall or both, indicating that most primary roots that emerged from the trunk did so when the tree was in the #3 or #15 container within 22 months of planting from rooted cuttings. Roots often grafted when crossed or laid against other roots, but roots did not graft to trunks.

Nursery Planting Depth, Mulch Application, and Root Pruning at Landscape Planting Affect Tree Health and Anchorage

“…Elms (not maples) planted deeply in containers in the current study were somewhat better anchored three to five years after planting (Figure 2); however, the significant but slight increase in anchorage is probably outweighed by the negatives. Placing the root collar more than a few mm below the surface encourages roots to grow over the collar of various Quercus, Ulmus, and Acer (Fare 2005;Gilman and Harchick 2008;Bryan et al 2010;Gilman et al 2010b) and perhaps other taxa not yet tested. These are considered a source of stem-girdling roots and future health problems (Wells et al 2006), thus Johnson et al (2008) recommend removing these at planting.…”

“…There is good evidence for reduced as well as for equal growth rate in the nursery when the root collar is installed deeply in container substrate depending on study location, planting depth, and taxa (Browne and Tilt 1992;Fare 2005;Gilbin et al 2005;Byran et al 2010;Harris and Day 2010). Gilman and Harchick (2008) and Harris and Day (2010) showed that certain taxa generate adventitious roots from the buried stem in the nursery container or after landscape planting from small containers. They agree that adventitious roots may function to aid in establishment of certain deeply planted young trees, although some taxa do not appear to have the capacity to grow new roots from the buried stem.…”

Container and Landscape Planting Depth and Root Ball Shaving Affects Magnolia grandiflora Root Architecture and Landscape Performance

“…This strongly suggests that magnolia did not have the capacity to generate roots from the root collar after landscape planting under conditions of this study. Others showed that roots ceased growing from the collar as trees became 24 to 60 months old (Coutts et al 1983;Lyons et al 1987;Gilman and Harchick 2008).…”

“…There is good evidence for reduced or equal growth rate in the nursery when the root collar is installed deeply in container substrate depending on study location, planting depth, and taxa (Browne and Tilt 1992;Fare 2005;Giblin et al 2005;Byran et al 2010;Harris and Day 2010). Gilman and Harchick (2008) and Harris and Day (2010) showed that certain taxa generate adventitious roots from the buried stem in the nursery container or in the early years after landscape planting from small containers. They agreed that adventitious roots may function to aid in establishment of certain deeply planted young trees, although some taxa do not appear to have the capacity to grow new roots from the buried stem (Lyons et al 1987).…”

The Management of Tree Root Systems in Urban and Suburban Settings II: A Review of Strategies to Mitigate Human Impacts

“…The structural roots can also be too deep in container-grown nursery stock if trees are not planted carefully at each repotting. A dense mat of roots can fill the soil above the woody roots that form the root flare (Fare 2006;Gilman and Harchick 2008;Gilman et al 2010b), and make it impossible to plant the woody roots at the correct depth without cutting away a substantial portion of the roots in the ball.…”