2 Gilman: Anchorage Influence by Production Method and Root Pruning application of water only to the top of the root ball consistently results in quick establishment from rapid root growth (e.g., Gil- man et al. 1994; Gilman et al. 2010a). Roots are not confined to the irrigated area attributable to ample soil moisture under mulch outside the root ball periphery (Stabler and Martin 2000). The present study compared anchorage and growth of planted container-grown trees considerably larger than previously tested with that of similarly-sized trees transplanted from a field nursery. A second study was designed to compare anchorage and growth of 1) recently planted trees irrigated only on the root ball with that of trees receiving irrigation over a larger soil area, and 2) recent- ly planted trees whose root balls were shaved or not at planting. MATERIALS AND METHODS Study One Thousands of live oak (Quercus virginiana Mill., ‘SNDL’, PP#12015 Cathedral Oak) trees began as cuttings stuck into square 14 cm tall × 6.9 cm wide smooth-sided containers (Anderson Die and Manufacturing, Portland, Oregon, U.S., model 03AN-BAN2_7-8 × 5) in August 2001 at Skinners Nursery (Crescent City, Florida, U.S., USDA Hardiness Zone 8b). Trees were shifted into 3.8 L smooth-sided containers (20 cm tall × 18 cm top diameter, Nursery Supplies, Fairless Hills, Pennsylvania, U.S.) in May 2002, and into either 57 L Florida Cool Ring containers (41 cm tall × 44 cm top diam- eter, Florida Cool Ring, Lakeland, Florida) in March 2003 or into a field nursery (Myakka fine sand, non-hydric). Trees in 57 L containers were planted into 379 L containers (51 cm tall × 91 cm top diameter) Cool Ring containers in Septem- ber 2004. Container substrate was 50:40:10 (New Florida peat: pine bark: sand, volume). New Florida peat is a compost of Florida peat and hardwood bark fines (Florida Potting Soil, Inc., Orlando, Florida). Fertilizer (18-5-10 controlled release, Harrell’s Inc., Lakeland, Florida) was incorporated at 10.74 kg/m3 into substrate prior to planting; additional fertilizer was periodically applied. Weeds were hand pulled from container substrate. Trees did not root out of pots and into the ground. All trees were pruned to one central leader twice annually. Three matching trees with trunk diameters of exactly 14 cm (measured with a diameter tape 8 cm from substrate sur- face) were chosen from both the field and container plots. Field-grown trees were lifted from the nursery January 2008 with a 152 cm diameter tree spade and placed in copper-treated natural burlap inside a wire basket that matched the root ball dimensions. Woven black plastic nursery ground cloth fab- ricated as a sleeve to fit over the basket was placed into the hole dug by the spade, and the root ball with basket was low- ered back into the hole inside the sleeve. The fabric prevents most roots from penetrating and growing into the soil outside the root ball facilitating easy lifting later. Certain segments of the wire basket were tightened around the root ball to main- tain soil contact with roots. Trees were irrigated several times daily to maintain turgor as standard practice in the region until March 2008. This practice of digging field-grown trees sev- eral weeks to several months prior to landscape planting is known as “hardening-off,” and results in trees that transplant reliably and with a high survival rate (Gilman 2001). It has been a common practice in the region for more than 20 years. ©2013 International Society of Arboriculture In March 2008, trees were planted 6 m apart into field soil several hundred m from where they were grown in the same nursery in a randomized complete block design with one tree from each treatment in each of three blocks. Holes were dug with a backhoe and the bottom was tamped by foot to stan- dardize settling. The top of the root ball was positioned even with the soil surface. Once the root ball was placed in the hole, a 15 cm wide volume of undisturbed soil at the edge of hole was loosened and pushed into the hole. The rest was filled with soil that came out of the planting hole. Water was added to settle backfill soil before packing firmly with a per- son’s foot. No berm or water ring was constructed around the root balls and no fertilizer was added during the study. A layer of hardwood wood chips 10 cm thick was applied as mulch to the root ball surface and adjacent soil in a 3 m diam- eter circular area around each tree. Mulch was absent in the 18 cm radius adjacent to the trunk. All vegetation was periodically killed with Glyphosate (isopropylamine salt, 41%) in a strip 4 m wide down each row with care to prevent spray on the trunk; veg- etation between rows was mowed. Fifty-seven liters irrigation was applied daily through four Roberts Spray Stakes (Roberts Irrigation Products, Inc., San Marcos, Idaho, U.S.) positioned at the edge of the root ball spraying toward the trunk to encourage rapid growth; no irrigation was applied to the soil around the root ball. Trees were staked to stabilize them in wind. Stakes were removed in October 2008 and trees pulled with a winch to 15 degrees trunk tilt from vertical start position as described hereafter. Study Two In August 2003, thousands of Cathedral Oak trees began as cuttings in the same nursery as described for study one. Trees were shifted into the same 3.8 L smooth-sided containers as in study one in May 2004, and into 57 L Florida Cool Ring containers in May 2005. Trees were shifted into 254 L Flori- da Cool Ring containers (40 cm tall × 76 cm top diameter) in November 2006 using the same substrate and fertilizer regime as study one. In March 2009, 24 trees with exactly 8.9 cm trunk diameter (measured with a diameter tape 15 cm above sub- strate surface) and a mean height of 4.7 m were chosen from the group of thousands of trees. Twelve trees were root pruned (referred to as shaving, Gilman and Wiese 2012) with a recip- rocating Tiger Saw (Porter-Cable, Inc., model 9748, Jackson, Tennessee, U.S.) by cutting tangent to the trunk to remove the entire periphery (approximately 5 cm) of the root ball (i.e., the sides and bottom). Although no data was collected on the diameter of the cut roots, most trees had cut roots up to about 2 cm in diameter at the periphery. The other 12 trees were not root pruned at planting. Trees were planted into the same field soil as study one in three rows of eight trees 4.9 m apart. Half the trees in each root pruning treatment were irri- gated with 44 L once daily. Water was applied only to the root ball surface through four Roberts Spray Stakes installed at the edge of the root ball directing water toward the trunk. The other half received twice the volume (88 L) through the same four stakes plus four more at the root ball edge which directed water outward away from the trunk onto the soil around the root ball. Total irrigated area for this treatment including the 76 cm diameter root ball was a circular 3 m2 . Plots were mulched and maintained as described for study one. Trunk diameter was again measured October 2009.
January 2013
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