In the July and August 2014 editions of American Nurseryman, the results from a root morphology study, as well as the results from an analysis of the costs of production, were published in relation to three different tree-related nursery production systems: IGFC (in-ground fabric container), PiP (pot-in-pot) and B&B (balled-and-burlapped) field-grown trees. Trees installed in urban areas of the northeastern United States are estimated to be overwhelmingly (90 percent) produced as field-grown specimens that are then dug, wrapped in burlap and transported to the new planting site as a B&B tree. Despite the high usage of this production method, differing and more novel nursery techniques are becoming increasingly popular in the Northeast, including PiP container grown, IGFC, as well as field-grown bare-root (BR) production systems.

The goal of this continuing work was to build on existing research and provide a more scientifically based understanding of the average cost of planting trees grown using these four different production systems in the urban environment, and to measure how these costs vary. This critical information may be applied by Tree Wardens, municipal arborists, and community foresters who routinely identify budgetary constraints as a key-limiting factor in relation to the management of urban trees.

Planting process

We began by obtaining 24 research swamp white oak (Quercus bicolor) trees from the Woodman Horticultural Research Farm in Durham, New Hampshire (courtesy of Dr. Cathy Neal). We also acquired an additional 24 red oak trees (Q. rubra) from Amherst Nurseries in Amherst, Massachusetts. The swamp white oak trees were grown at the Research Farm using three production methods: eight as field-grown B&B, eight as containerized PiP trees, and eight as IGFC. All red oak trees were grown at Amherst Nurseries using three methods: eight field-grown, harvested as B&B, eight IGFC and eight field-grown, harvested BR.

A hole is augered in preparation for tree planting.

Image Courtesy Of iStock | Richard W. Harper

Three individuals (nursery employees and University of Massachusetts researchers) initially loaded the B&B trees onto landscape trailers using a tractor; trees were then rolled into position and secured to the trailer using rope by the employees. PiP and IGFC trees were loaded onto the trailer by being lifted from the ground by two employees, with one employee located inside the trailer to position and secure the trees. BR trees were loaded by hand in like manner, requiring only one individual to lift each tree and another to secure the trees on the trailer. The roots of all BR trees were moistened and loosely covered with burlap to help protect against desiccation.

Once the loading was completed, three employees unloaded the B&B trees at the planting location, requiring a utility vehicle fitted with an auger attachment, to lift and move the trees. PiP and IGFC trees required two employees for unloading, consisting of an operator to drive and an employee to walk beside the trailer, unloading each tree at its planting location. BR trees were kept on the trailer under the protection of the tarp until the planting holes had been dug, to which they were then carried.

To minimize the number of external factors affecting planting costs, the same crew, using the same equipment, planted all the trees in Amherst in three workdays (May 14 to 16, 2014). All trees were installed by two employees using the same process, except in the preparation of the root ball, which differed in accordance with the trees’ respective production system.

Each planting preparation process began in the same manner: by measuring the distance between the beginning of the root flare and the bottom of the root ball, to determine the proper planting depth. The sides of the planting hole were scarified to facilitate root penetration into the surrounding soil profile, and to encourage successful tree establishment. Any notable dead or damaged branches on the trees were removed. The root ball was then prepared for planting in the manner appropriate in relation to its respective production method.

For B&B trees, the wire cage and burlap were removed from the root ball; PiP trees had their container removed from the root ball, and roots were pruned with hand pruners and a saw; IGFC trees’ fabric bag was removed from the root ball; and BR trees were root pruned to remove dead or damaged roots, if needed.

Each root ball was then placed into its prepared hole. The hole was backfilled to about half of its depth and ”watered in,” to help remove air pockets and anchor the tree in place. The hole was then backfilled the rest of the way and watered a final time. A water-well was shaped around the base of the trunk and a 2- to 3-inch layer of bark mulch was then applied.

Which method?

Workers plant a tree in its designated hole.

Image Courtesy Of iStock | Richard W. Harper

We used our findings of planting costs and time to determine which planting methods are most efficient. A key factor in determining the planting cost of an urban tree is planting time, as it determines both labor and equipment costs. Thus, we pooled data for the two species of oak and tested for differences across production systems. Planting times were determined to vary according to the size of the tree and the production system; the difference between the two tree species was not significant. B&B trees required that the wire basket and burlap be removed, IGFC trees required the fabric container be removed from the root ball, and PiP trees were removed from the plastic container. PiP trees sometimes required extensive root pruning to address root girdling. With these differences across types of trees and differences in tree weights and root ball sizes, we observed variation in the time required to plant the trees.

The greatest planting time, on average, was for the B&B trees at more than 900 seconds (Table 1), which was significantly greater than mean planting times for all other methods. On average, the BR trees were planted in less than half that time at 428.6 seconds. IGFC trees averaged a planting time of 517.1 seconds and the PiP trees required an average 675.1 seconds.

Planting costs per tree were estimated using the data collected for time unloading, digging holes and planting. This also included the labor and equipment required to dig holes, to place the tree at the site, and to complete the planting process. The costs to dig all holes included the rental costs for a $35 per hour machine with an auger attachment and a $26 per hour equipment operator.

The costs of unloading and placing each tree at the planting site included the costs of a pickup truck at $10 per hour, trailer at $3 per hour, and operator labor and an employee at the equivalent wage rate of $13 per hour.

The costs of unloading the trees differed by tree production type. B&B trees included the costs of the pickup truck and trailer, the machine to move them to the holes, operator labor and an additional employee to help move the trees. All other tree costs only consisted of the truck, the trailer, and the labor costs of the two employees. The cost per tree for B&B trees was $3.43, the cost of the IGFC and PiP trees was $0.58 per tree, and the BR trees cost $0.22 per tree (Table 2 on page 18).

The final component of costs was planting the trees themselves. The planting times for B&B trees were noted to be statistically greater than the times for all other methods, and that time translated to a planting cost per tree of $6.51. The B&B planting costs per tree were $1.64, $2.78, and $3.42 greater than PiP, IGFC and BR trees, respectively. Since variation in planting sites may be widespread, travel time was not a consideration as part of this study, nor was market purchase price of the trees relative to the differing production systems.

Read more: Costs of Growing River Birch in Different Production Systems

Conclusions

There are substantial differences in the costs of planting trees, and in this continuing research, we showed that these costs can differ significantly due to nursery production methods. Mean comparisons showed that when hole preparation was complete and all trees were placed next to the holes, the mean planting time for B&B trees was significantly longer than mean times for PiP, IGFC and BR trees, and the mean BR planting time was significantly shorter than all other treatments. The mean planting cost per tree for B&B trees was also found to be the most expensive, followed by PiP and IGFC, with BR being the least expensive tree to plant.

Our research demonstrates that although field-grown B&B production has historically been the standard nursery method in the Northeast, planting times and costs for B&B trees may be more expensive and time- intensive than trees produced using other nursery production methods.

Read more: Production Effects on Tree Root Growth and Morphology