The most common container type for nursery tree production
is black plastic (BP). Root injury sustained during production may negatively
affect tree health when planted in the landscape. Research at Colorado State
University is using Pyrus calleryana Decene.
‘Glen’s Form’ (Chanticleer®), comparing trees grown in BP to two fabric
containers: Root Pouch® (RP) (Averna & Associates, Hillsboro, Ore.) and
Smart Pot® (SP) (High Caliper Growing-Root Control, Inc., Oklahoma City, Okla.).
Trees were planted into the landscape, after being grown in a nursery
production setting, in fall 2010, spring 2012 and spring 2013; trees will be
fully excavated and harvested (after one, two and three growing seasons) to
compare transplant success based on growth measurements (e.g. root and shoot
re-growth, leaf area, height, caliper and branching measurements).
Post-transplant success of trees will be determined during the growing season
using pre-dawn leaf water potential and infrared leaf canopy temperature. In
2011 and 2012, there were no significant container effects on height, caliper,
root:shoot ratio and dry leaf, shoot and root weight. In addition, there were
no container effects on pre-dawn leaf water potential and infrared canopy
temperature. However, in 2012, there was a significant difference for average
root re-growth beyond the original root ball: BP had 17.5% root re-growth
compared to 30.2% and 29.4% for RP and SP, respectively. There were no significant differences for
root re-growth in 2011 (8.4% BP, 10.6% RP and 10.2% SP). Though there were no
significant differences in above-ground growth, nor dry root weight, root
re-growth and visual root architecture differed among the three container
types. One preliminary conclusion from this study is that you cannot predict below-ground
establishment potential based on above-ground growth. Another conclusion is
that planting to BMP standards is unlikely to correct problems caused by container
type in the nursery. This research will continue to investigate root re-growth
over multiple seasons.
Another component of this research
is investigating evaporative loss from the three container types to determine
if RP and SP containers have a great irrigation requirement than BP. During
winter 2013, we conducted two greenhouse studies to measure evaporative loss from
containers. The first study examined evaporative water loss among the three
container types during a single dry-down from field capacity. In the second
study, we wrapped RP and SP containers in plastic to prevent evaporative loss
from the outside container surface, and compared this to unwrapped RP, SP and
BP. Containers were weighed to determine daily water loss, and volumetric water
potential using frequency domain reflectometry was measured. Preliminary
results show that fabric containers lose water more quickly compared to black
plastic and may require more frequent irrigation under production conditions. We
will also conduct these experiments using plant material to determine how
transpiration affects container water loss.