By Matthew Stephens
In the fall of 2015, New York City completed its ambitious MillionTree initiative two years ahead of schedule. This was a public/private partnership that planted one million trees throughout all of New York City. Trees were planted throughout world-famous parks, up and down hundreds of miles of streets, and in the backyards of many New Yorkers. New York City is certain to become greener as these newly planted trees flourish.
New York City’s street tree program is the world’s largest, and plants approximately 20,000 street trees each year. Given the East Coast climate of hot summers and cold winters, planting seasons have been established to organize tree planting into two seasons, which both last approximately 10 weeks in spring and fall. Therefore, the goal each season is relatively straightforward: plant 10,000, 2.5- to 3-inch-caliper trees each season in a 10-week period with the help of a cadre of local landscape contractors. One of the many challenges associated with this goal is ensuring every tree is planted at the “right height.” New York City defines the right height as the location where the root flare is just visible peeking above the soil line. It is a point where the first two or three structural roots can be found on every tree. Through the years, program managers had tried all sorts of creative mechanisms to ensure every tree was planted correctly; however, none of them seemed to be fully reliable — until a bright spring day when progress was made.
One day while I was out visiting our planting operations, I saw one of our skilled landscapers carefully removing the soil on the top of a rootball to expose the root flare prior to installation. I watched carefully as the landscaper skillfully removed inch after inch of soil looking for the first two or three structural roots. However, in this instance, he found that the root flare had been buried six inches deep in the rootball. At this point in the planting process, the rope and top of the rootball cage had already been cut away as he searched for the root flare, and the tree was in the planting hole, now sitting about six inches too deep. The challenge for the landscaper then became to figure out a way to raise the tree carefully to bring up the root flare level with the surrounding grade. The landscaper then went about with a colleague and some mechanical muscle to raise the rootball of the tree. It was a precarious process at best, and ultimately the rootball was raised, although the remaining rootball had become loose and some roots had been broken. I looked around at the planting site and saw the twine mounded up in a ball, a bit of the rootball cage cut away and a giant pile of soil that had been taken off the top of the rootball in the search for roots. I thought about that giant pile of soil that had no roots, and immediately felt that we had been cheated out of a finished product. I thought to myself, why did we pay full price for a tree, when only half of the roots were present? It was that moment when I had an epiphany — we were focusing on root flare depth at the wrong stage in the tree installation process. Root flare depth in the rootball can be fixed by the tree grower much more easily than by the tree installer.
Therefore, New York City engaged its tree growers in a discussion about how trees that were harvested for NYC Parks could have the root flare exposed before it was dug out of the ground at the nursery. What this discussion led to confirmed that this was not only possible, but there is one big benefit in making sure the root flare is exposed prior to digging — more roots are dug with each tree. When the root flare is uncovered prior to digging, the tree spade that digs the tree out of the ground is able to encase more roots within the rootball instead of leaving them in the ground. Conservative estimates seem to indicate that an additional 20 to 30 percent of roots come with the newly harvested trees when the root flare is exposed first. In addition, knowing that 90 to 95 percent of roots may be cut during the tree harvest process means that an extra 20 to 30 percent of roots that do come with a tree can make a huge difference. In addition, New York City also noticed that once trees were being harvested with the root flare visible, the entire rootball became more stable and solid during the transportation process from the nursery to its final planting location.
After the discussion with tree growers, New York City’s enforcement technique became simple with tree growers. The City didn’t tag a tree to be dug for the tree planting program if the root flare was not visible. If it was a beautiful tree with a perfect canopy but the root flare was not visible at inspection time, the tree would be overlooked. This immediately led to our tree growers ensuring the root flare was visible for each and every tree prior to us making our tagging arrangements. It is important to note that current nursery standards (American Standards for Nursery Stock- ANSI) clearly note this should occur for every tree, but does not occur consistently throughout the profession.
What also became immediately clear is that if the root flare was made visible during harvest, it directly translated into another benefit — but one for the installation contractors at the time of planting. No longer were landscape contractors spending time and labor at each tree trying to figure out where the root flare was (a delicate process that requires removing soil carefully, and then raising or lowering the tree to get it at the right height). Now that the tree growers were responsible, the landscape contractors could see time and time again the root flare was at the top of the rootball. When they pulled back the twine and burlap that covered the rootball during transportation, the root flare was always in the exact same location. This led to increased productivity each day, and more trees were able to be planted in a single day. In addition, after tracking closely for a few years, NYC Parks also noted a decline in the overall mortality rate for all trees during the first two years after planting.
Every tree purchaser must advocate for the root flare to be made visible prior to harvest. However, one large item to consider in this process is that this may be a large business process change for many tree growers (rarely have they been engaged in root flare discussions). NYC Parks asked if other customers had been asking for the same treatment, but found that few tree purchasers ever ask about root flares. Therefore, landscape contractors, urban foresters, wholesale buyers and landscape architects all have to start asking their tree growers to address root flare depth in the nursery for meaningful change to occur. Tree growers must also raise their standards and ensure the root flare of every tree dug is visible prior to digging. Without this group of tree purchasers holding tree growers accountable, it is unlikely to expect change will occur. In addition, tree growers should use this as an opportunity to diversify their product from their competitors, given that there is mounting proof that exposing the root flare prior to harvest results in more roots coming with the tree — and ultimately lower mortality. Almost anyone would gladly pay a higher price for a tree with more roots and a lower mortality rate. Therefore, the only question that remains is: how deep is your flare?
Matthew Stephens is garden director for the San Francisco Botanical Garden and Conservatory of Flowers. Prior to his role in San Francisco he worked at NYC Parks for nine years where he led the Tree Planting Program and oversaw the MillionTrees initiative. While at NYC Parks, Stephens worked to increase the overall efficiency of the tree planting program, implemented a platinum-level customer service program, led the development of NYC Parks’ innovative tree procurement program, and raised millions of dollars in private funding for the urban forest.