The Truth about Tree Boxes

ffytNow that tree planting time has arrived, I just finished two Citizen Forester classes at Casey Trees and came away with this startling revelation: Our city’s tree boxes are all wrong.

We pass tree boxes everyday, everywhere. They are those rectangular spaces between the curb and the sidewalk where typically a tree has been planted and typically some neighbor has boxed in the box with 4 x 4s or 2 x 6s, poured in more soil and tried to grow a bumper crop of pansies or irises or even sunflowers. Sometimes the barriers are more elaborate: wrought iron, say, or decorative metal posts with black chains strung in between. And sometimes the plantings include exotic grasses or ivies or, in many cases, just a tall bunch of weeds.

Truth is all of that stuff is bad for the trees and bad for the city. I’ll explain why in a moment. Suffice to say, the best thing we could do with those tree boxes is simply apply a layer of quality mulch to hold in moisture and inhibit weeds. Then water the tree on a regular basis and leave it alone.

You’ve all wondered, I’m sure, who keeps planting all these trees and why many of them seem to wither and die. Well, as we learned in Citizen Forester class, that strip between the curb and sidewalk that exists just about everywhere in the city is the domain of a small agency called the D.C. Urban Forestry Administration. This agency used to be under the Department of Public Works.  But it was moved to the Transportation Department, enabling the city to use federal highway funds to plant trees.

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As you know, the city has lost much of its tree canopy in recent decades. Trees are vitally important to create shade in the summer, provide habitat for wildlife and turn the greenhouse gas carbon dioxide into oxygen we can breathe. Trees also transpire moisture into the air that later becomes rain. Mature trees lining a street or avenue even have a calming affect on traffic.

Almost all of the trees planted in tree boxes are the responsibility of the Urban Forestry Administration (UFA).Except the city doesn’t plant all the trees. That is the job of one contractor hired by the UFA.

Many of the trees don’t survive.  Sometimes, explained Urban Forester Duff McCully, that’s because the tree was planted improperly. Sometimes mulch is piled up like a volcano around the base of the tree, starving the tree of water or making a home for disease. Some trees are run over by cars or destroyed by rough-housing kids. Sometimes trees are killed by people who just hate trees. (Hard to believe, but McCully insists that not everyone is a tree lover.)

Mostly, though, newly planted trees fail to survive the critical first two years because people don’t water them, and are doing all kinds of wacky “gardening” things to the tree boxes. (You thought the city was responsible for watering those young trees? Think again.)

For instance, any barrier, whether wood or metal, that is placed around the tree box prevents water from running off the sidewalk and into the box. Not only does this deprive the young tree of water it needs to survive, it means more water running into the storm drains, carrying pollution into the watershed. These days, we need all the open soil we can get so that water finds its way back into the earth rather than carrying pollutants into the Chesapeake Bay.

Often after a would-be gardener builds his box around the tree box he then piles in more soil to create a place to plant flowers or shrubs. But the extra soil starves the young tree roots of air and water and creates a perfect environment for disease to attack the tree. In addition, plantings such as most perennials, grasses and ivies create a matt of roots that further restrict the flow of air and water to the tree’s roots.

The final irony: the stuff the gardener plants in the tree box often dies from neglect. How often do you run a hose out to your curb? Then after everything in the tree box is dead, the box becomes a perfect receptacle for beer bottles and other garbage.

If planting anything at all in a tree box, the best choice is some small annuals around the edge of the box. Otherwise, the ideal approach for a young tree is to cover the area with a 1-inch layer of mulch, such as cured hardwood chips or bark. Don’t mound the mulch in the middle. Mound it around the edges to create a saucer shape so that water runs from the outside of the box toward the tree.

Water the tree regularly, especially during hot weather when trees are transpiring like mad.

Casey Trees is working on a more perfect tree box design. D.C. Urban Gardeners will be doing what it can to get this message out to the public and help save our young trees. Do your part by not trying to create a garden in your tree box. And give your tree the water it needs .

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