Thomas J. Brass, Gary Keever,
Charles H. Gilliam, and D. Joseph Eakes
negative factors associated with container production of nursery
high root-zone temperatures and root circling along the substrate-container
interface. Temperatures can reach 122oF in nursery
containers in the southern United States, due to direct solar
radiation striking the container sidewalls. Elevated root-zone
temperatures in excess of 104oF may lead to root injury
or death, reduced shoot growth, and higher transpiration rates.
Root malformation and circling in containers are common for trees
with vigorously growing root systems. These conditions may lead
to a less fibrous root system, a reduction in plant growth, or
the formation of girdling roots which contribute to poor root
regeneration and slow transplant establishment in the landscape.
Copper compounds sprayed on the interior surface of containers
control root malformation and circling. As a result, root malformation
and circling are reduced, permitting increased root regeneration
Flowering dogwoods are naturally found in partial shade in well-drained,
organic soils with roots maintained in a cool, moist environment.
When dogwoods are grown in containers on beds exposed to full
sun in the Southeast, root-zone temperature becomes an important
factor. Several growers have expressed difficulty in producing
container-grown dogwoods, presumably due to high substrate temperatures.
This study examined the response of dogwood when grown in styrene-lined
and/or copper-treated containers.
An experiment which included all combinations of two dogwood
cultivars, +/- styrene lining, and +/- copper coating was established
on March 13, 1993. Styrene sheeting, 0.1 inch thick, was inserted
into 3-gallon nursery containers covering the sidewalls but not
the container bottom. Copper hydroxide at 13.4 ounces per gallon
of latex base (Spin Out) was applied with a paint sprayer to
the containers interior surfaces or directly to the styrene,
which was later inserted into the container. Uniform liners of
Weavers White dogwood, an early bloomer in
south Alabama, and Bartons White dogwood, a
Tennessee selection that blooms about a week later, were planted
into containers using amended pinebark:sand substrate and grown
in full sun.
Data on shoot and root growth were collected in July and December
1993. Four plants receiving each treatment were repotted into
their original treatment containers to determine residual effects
of copper on root suppression and copper and styrenes effects
on growth of plants held for a second growing season. Six plants
from each treatment were repotted into 7-gallon, non-treated
black containers to determine treatment effects on new root growth
outside the original rootball.
Treating containers with copper effectively
reduced root circling at the substrate-container interface in
both cultivars. However, plants grown in containers treated with
copper had less root dry weight during the first years
production and less growth in height during the second season
compared to those grown the first season in non-copper-treated
containers. Both cultivars repotted into 7-gallon containers
had less trunk diameter growth and a lower percent surface root
coverage when previously grown in containers treated with copper
than in containers not treated with copper. Copper treatment
also reduced root dry weights during the first year of production
but had no effect on dry weights of newly generated roots outside
the original rootball following repotting.
Dogwoods grown in styrene-lined containers had a greater percent
surface root coverage and less root dieback during the first
and second growing seasons in 3-gallon containers, in addition
to greater growth in height during the second season. Plants
originally grown in styrene-lined containers had more trunk diameter
growth and a higher percent surface root coverage after being
repotted into 7-gallon containers than those grown in non-lined
containers. While substrate temperatures were not monitored in
this study, the reduction in supraoptimal substrate temperatures
by styrene lining, and the concomitant beneficial effects on
plant growth from such a reduction have been previously reported.
These results demonstrate potential beneficial effects of styrene-lining
to dogwood, a species sensitive to supraoptimal substrate temperatures.
Percentage of Surface
Root Coverage at the Substrate-container Interface