Not Your Grandmother’s Tree Box

How one Capitol Hill block is caring for its tree boxes
Photograph By
Laurie Duncan

Nick Waterson and son Thomas. Photo: Laurie Duncan

Please don’t call them tree boxes.  These curbside amenities have been re-branded “tree spaces” because now we know that trees need more than a little square of soil in order to survive and thrive. These spaces can make a street look shabby or sharp, yet in DC, their care rests solely on what amounts to the kindness of strangers, as the city does not maintain them. Here’s the story of how one Capitol Hill street is taking on the tree space challenge.

Let the E Street, NE Tree Space Games Begin

Last summer, the city vastly enlarged the tree spaces on 1200 block of E Street Northeast to help its new trees grow. This work was largely instigated by resident tree-advocate Mike Ikenberry. All of a sudden, thousands of square feet of bare soil appeared along the curb in a bold act of concrete removal. Good for the trees? Yes. But what should be done with this new expanse of virgin soil? Nature abhors a vacuum, and weeds quickly moved in while residents weighed their options.

People on this street are neighborly. They have a list serv, they have pot lucks, they know one another’s kids, and they organize. Last September, E Street resident Laurie Duncan invited me to give a talk in her home on tree space planting options. Around the dining room table I talked with a dozen or so home owners about regulations, street tree fences, dog pee, and plants beyond the ubiquitous Liriope (aka lilyturf) that could survive this tough environment. The group soon realized that this job would require a lot of plants. They declined the option to install turf, not wanting this demanding and unsustainable option. While they thought more about it, a long, snowy winter ensued.

In spring, Ms. Duncan was ready to tackle the project. Her corner home had the largest tree spaces, 400 square feet on E Street alone. I provided a short list of suitable plants and a sketch with their layout and approximate arrangement. Over the next two months, Hill gardener Susan Borchardt translated my plan into measured drawings with precise quantities. We made some plant substitutions in an effort to select only the toughest candidates. Along the way, Ms. Duncan’s enthusiasm attracted a few more residents to participate. By June the project was ready to roll. Ms. Borchardt ordered the plants and rented a van to pick them up. Soil amendments and mulch were reserved at Frager’s. One gorgeous Saturday, over a dozen residents and kids spent the entire day working. 

DCMR Title 24, Section 109…and other Regs 

Of course there are regulations about this sort of thing, nowhere as glamorous as the April 2014 publication, “Greening DC Streets,”  http://ddot.dc.gov/publication/greening-dc-streets, which illustrates the shape of things to come, the humble DC Municipal Regulations address “Beautification of Tree Spaces” http://www.dcregs.dc.gov/Gateway/RuleHome.aspx?RuleID=1241714

Here’s what you need to know: 

  • Planting tree spaces does not require a permit;
  • Property owners pay for and maintain the work;
  • Keep plants away from bus stops, alley entries, fire hydrants, and parking meters;
  • Don’t change the grade of the soil (that’s bad for trees);
  • Use plants that grow no taller than 18 inches; 
  • Plant no vegetables (dogs pee in tree boxes despite our best intentions);
  • The District may “remove or destroy” plantings with “sufficient notice” when needed for construction.

Another publication, the very useful 2011 ”DDOT Public Realm Design Manual,” adds that “plantings should be a minimum of 2 feet from the root flare of the street tree in order to protect feeder and anchor roots from damage.” See section 3.6.4 in website: http://ddot.dc.gov/page/tree-fence-specifications-astm-787-astm-653-and-astm-607

Design Matters

The District’s regulations are good at telling you what not to do. Here are some ideas of what to do, and why. If you’re looking down a long street that gets a lot of sun, like the south side of the 1200 block of E Street, NW, tree spaces that are now 25 to 40 feet long and nearly six feet wide command a strong presence. If the trees set up a rhythm like a bass guitar, plantings in the tree spaces play the melody. Imagine walking down a street where a predictable repetition of elements at ground level mirrors that of the architecture above. There is comfort in this type of urban landscape. 

To achieve predictability while avoiding monotony, I recommended a limited plant palette of just three species:

  • Pennisetum alopecuroides ‘Hameln’ (Dwarf Fountain Grass). Early flowering, 18”-24”, clump forming, flowers July through September. Cut back in March to 4” from crown of plant
  • Carex flacca ‘Blue Zinger’ (Blue Sedge), height 12”-18”, blue-green foliage, cut back in March, native.
  • Sedum ternatum (Three Leaved Stonecrop) Evergreen leaves in whorls of three. Delicate star shaped flowers in May-June, height 6”, native.

In order to establish a sense of intentionality, the Dwarf fountain grasses were used at the outside edges of each tree space like a frame. Then the Blue sedge and Stonecrop sedum were inter-planted in groups toward the center. The tree root zone was left unplanted for 4’-6’ on either side of the tree trunk. This area was mulched, and mulch was kept several inches away from the trunk itself to discourage fungus, insects, and other pests.

Note that while the Carex and Sedum tolerate shade, you would use something other than the Pennisetum on the shady north side of the street. There I would consider Euphorbia amygdaloides var. robbiae (Wood spurge), which is evergreen and can take sun or shade. 

One of the benefits of a limited plant palette is that each tree space does not have to be identically replicated in order to achieve the sense of repetition. Another is easy maintenance, since it is clear what plants are intended to be there, and weeds are more easily identified. A smaller plant palette also makes purchasing more cost effective as you are getting more of the same species, and wholesalers like to sell in multiples of 12 or more.

A Helping Hand

A combination of advocacy, organization, expertise, planning and elbow grease helped the E Street NE tree space project take shape. While adults worked and kids played in the mulch with toy dump trucks, Susan Borchardt kept volunteers on track by setting out plants according to plan at the correct spacing, and showing people how to plant. All neighbors worked on one tree space at a time, and the group moved down the street together. Mr. Ikenberry weeded and mulched tree boxes that were not planted this time around. Passersby asked if the group could help plant tree spaces on their street (“sorry but no”), and some apartment dwellers who just liked getting their hands dirty took part as well. The group planted 125 plants, amended the soil and mulched for eight hours. Then one neighbor made dinner for everyone as they kicked back and admired their work. 

Cheryl Corson is a licensed landscape architect who believes that nurturing a tree for a decade or more is good for people and the planet. She is in private practice on the Hill and beyond. www.cherylcorson.com


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