Bare Root Transplanting in Nathan Phillips Square, Toronto

Issue: 
July-August 2012

Step 1: Accessing & Protecting the Roots
The first step in the process was to remove the sod over the existing drip zone so that we could save the root mass. Next, we used an air knife to create a perimeter 1 foot deep and 6–8 inches wide (see above photo). This allowed us to ensure that no major roots were lost in the transplanting and to make a clean cut on larger roots to help prevent further desiccation. 

Once we established the root zone for moving the tree, we dug a larger trench around the perimeter. This allowed us to blow down and in to the trench to continuously move soil out the trench with the skid steer. We uncovered all the roots and pig-tailed or braided them to help minimize damage during transportation and retain moisture. 

As the roots were braided and tied to the trunk, we were able to move the trench toward the apex of the tree allowing us to continue to blow air down into a newly cleared trench. Keeping the roots moist throughout the process was a constant battle; we misted the roots every 20 minutes. Once the soil was removed from the majority of the root plate, we used a crane or large skid steer to break the taproot. Then we wrapped the attachment points in burlap and foam to avoid damage to the bark and/or cambium. 

Step 2: Moving the Trees to Their New, Temporary Environment
We used a skid steer to move the trees to the temporary hoarding zone. Before placing the trees in the pea gravel, we used our compost tea truck to add a rooting gel to the entire root system. This helped the roots to stay moist and added mycorrhiza. We quickly learned that the pea gravel held more water than originally thought, so we reduced the watering schedule to one hour per week. We also added 1 foot of mulch for the winter to avoid frost damage. We removed the mulch at the beginning of the spring to avoid cooking the roots. 

Originally, landscape fabric was applied to bottom of the pea gravel planting bed to stop the roots from travelling into the soil below. This proved to be inadequate so a much thicker material should be used in the future. Be sure to use a porous material that allows water to filter through so that you don’t create a drainage issue. The trees were in the pea gravel for 18 months, which was more than enough time to create good root growth (though the optimum length would be one full growing season). 

Step 3: Returning Them Home
When we were ready to replant the trees, we used a larger air knife with a larger compressor to move the pea gravel to allow us to lift the trees. We used our 100 ft, 30-ton crane to move the trees to their new planting sites with ease (see main photo on page 17). All trees went into new soil with higher organic matter with better nutrient cycling and water holding capacity. We planted the trees proud to allow for settling of the bare root system. Also, a heavy watering was applied to allow soil settle around the lower root system.

Parting Comments & Lessons Learned
This was a very innovative project with the potential to improve tree defects underground, soil and growing conditions, and move trees out of urban construction sites to be replanted after construction is complete. Although we didn’t plant these trees within silva cells due to budgetary restraints, the relocated trees were planted throughout Nathan Phillips Square in raised planters or in existing green space. Due to the improved size of the root systems, I believe that all trees replanted will be successful for years to come. Our overall success rate was 79% and we learned a lot about holding trees in pea gravel and the specific site requirements for success. Three oak trees did not survive the overwintering time in pea gravel. Possible reasons include overwatering, the fact that they were in full leaf when they were moved due to the early spring, and they were placed in full shade in the temporary hoarding zone. 

There are pros and cons to the method we employed here versus conventional tree spading. Bare root transplanting requires four to five people on site, several pieces of equipment, and long days. The pros are that you can retrieve about 90% of the root mass, repair structural flaws within the root system such as girdled roots, and improve compacted or nutrient deficient soils. Another positive of this project in particular was the increased root size due to holding the trees in pea gravel. This is not possible with conventional tree spades. However, tree spades are quicker, less expensive, and have a smaller carbon footprint.

This project was a great learning experience for Shady Lane Expert Tree Care and we are very pleased with the outcome. As arborists, we are often hired to remove healthy trees from construction sites in urban areas. For large-scale projects, this technique offers a viable alternative to tree removal, creating the potential for growth within our industry.  

Our mission is to enhance and promote the care and benefit of trees for present and future generations in Ontario through education, research and awareness.