City trees lead a hard life struggling with tree grates, strangles by light wires, and collecting cigarette butts

By TreeSteward Richard Fontwengler

In March of this year teams of Tree Stewards fanned out along the Rosslyn-Ballston corridor to inspect street trees growing in planter pits with tree grates.  Arlington County, short on resources to survey the condition of tree grates, requested help in identifying those trees that were having problems living within the often limited space provided by the grates.

Vincent Verweij, Arlington County Urban Forrester, saw this project as a “fantastic educational opportunity for Tree Stewards and a clear assist to the county’s efforts to protect and maintain street trees”.  With the Tree Stewards doing the assessment Arlington could used its limited resources to remedy any problems found and reported by the teams.

Trunk damage caused before grate was enlarged

The teams counted and inspected 194 grates in the corridor and found that almost 60% (101) of the grates were found to need attention with 12% (22) overgrowing the grate, 21% (38) touching the grate, 13% (24) had roots lifting the grate, and 14% (27) had grown to within one inch of the grate and would need attention soon.

The findings highlight the potential problems of using grates in the first place.  While they do provide trees with some protection from compacting soil around roots and damage to the base of the trunk, too often they are not monitored and maintained properly.  Also, many of the grates had surprisingly small center holes so if the tree was not planted dead center in the planting pit, or was lucky enough to thrive and grow large, it was doomed to eventually come in contact with the grate.

Tree Stewards were able to see the evolution of tree grate design over the 30 years or so the grates have been used in the Rosslyn-Ballston corridor.  Styles ranged from the traditional heavy cast iron grates to those made of lighter metals or plastic/composites.  Some were more ornamental and some were more functional.  Virtually all the grates we inspected were installed by developers as part of their projects which accounts for the variety of grates found.

An example of a larger soil panel with sectioned grate that is easy to enlarge.

As a result of the problems we observed with tree grates and the continued threat to girdling and damaging street trees planted within grates, Vincent is now recommending that developers of new projects use simple soil pits without grates for their street tree plantings.  The county is also asking developers to do a better job maintaining their tree pits and street trees after completion of their projects.

Larger spaces are provided for tree roots in the “soil panels” now required

Armed with the Tree Steward’s spread sheet report, the County Urban Forrester was able to enter the locations of trees/grates that needed attention and/or removal on a map for the maintenance crews.  While some of the grates can be modified to increase the size of the center hole most must be removed when a tree makes contact with the grate.  The crews are working through the list as they have time and most of the offending grates have now been removed.  In one instance the grates were part of a recent development and the developer was asked to do the work.

Large soil panels can also have flowers as a deterrent to walking on tree roots.

All in all a successful project and a perfect example of Tree Steward volunteers and the county working together in partnership to maintain and protect a most valuable resource:  street trees!