Blog Post By Carol Herwig

Elm Pruning Workshop Recap

Twenty Casey Trees Citizen Foresters, staff members and other volunteers joined National Park Service horticulturist Barry Stahl on Saturday, January 8, for a tree pruning workshop at Daingerfield Island. This wooded land just north of Alexandria doubles as a boat marina and tree nursery for the Mall. Stahl propagates elms from cuttings: at present, he’s growing the original American Elm species Ulmus americana, the disease-resistant cultivars Valley Forge, Princeton and New Harmony, plus the Jefferson and Washington elms.

Citizen Foresters work together to prune elms.

Our job was to prune up the young trees, generally 10-12 feet tall, nipping out dead and broken branches, removing too-low branches, establishing strong central leaders (that is, leading branches) and helping young trees get ready for their starring role on the Mall. This takes years and more than one pruning session. Casey Trees’ visit to Daingerfield Island has become a regular event on our winter calendar.

Stahl began the morning workshop with background on the various elms cultivars. The Jefferson and Washington cultivars have more rounded shapes than the others; the original Jefferson stands near the Freer and Sackler galleries and is distinctive for its rounded crown and because it greens up early and holds its leaves early; the newest elm in front of Natural History is a Jefferson, and the White House is getting a Washington. Stahl believes that there is no street tree quite like the American Elm and his passion and commitment to these trees comes through clearly.

Elms on Daingerfield island, nearly ready for planting in the District.

He explained there are no secrets to the Park Service’s Dutch elm disease maintenance plan. It is labor-intensive diligence with annual spring inspection and quick removal of diseased branches. Then we went to work, learning whys and hows of pruning. We prune in winter because the plant is dormant and so are the insects and diseases that can enter a tree through a pruning wound. Also, the tree’s structure is revealed. Conversely, late fall, when the sap is still running, is the worst time to prune.

Stahl teaches the three-part cut and the six steps of pruning. These include the five basics, plus one special one:

  1. Remove broken, diseased and dying branches.
  2. Select or create a central leader and cut back or remove competing branches.
  3. Select and establish the lowest permanent branch (depends on the tree’s location).
  4. Select scaffold branches and remove competing branches and plan for proper spacing
  5. Select temporary branches below the lowest permanent branch.
  6. Before you make a single cut, feel the ground, address the tree, walk around it and touch it.

With that, we went to work, bundling up with mufflers and handwarmers and armed with pruners, loppers and handsaws. We looked, we asked questions and we cut – carefully, thoughtfully.

Climbing a ladder to make a careful cut.

Warming up in the greenhouse afterward, we saw one- to three-year-old elms that are cared for indoors, to be planted outside when their time arrives. These young elms are closely cultivated, growing quickly, perhaps one day to stand among the magnificent trees on the National Mall.

Very young elms in the greenhouse.

We will be repeating the program on January 22 – please contact Carol Herwig if you are a Citizen Forester who would like to attend.

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