At the beginning of January, I fretted about pruning in the cold winter. The thought of climbing up a six-foot ladder to reach a couple of branches in freezing temperatures gave me the shivers. But to my surprise, it has been a pretty warm pruning season. The average temperature on a working day in January was 49 degrees Fahrenheit, and the last day of the month was 65 degrees. It was so warm it felt like we should have been planting trees — not pruning.

The warm weather has made pruning more enjoyable. I spent more time with the tree, finding defects to fix and enhancing the structure of the tree, instead of hustling to get back in the warm truck.The first month of the new year is behind us. The field crew’s work in January focused on American elms — both planting and pruning. So far we have pruned trees all over the District, along corridors like Massachusetts Avenue, Piney Branch Parkway, East Capitol Street and Nebraska Avenue. We have touched 300 trees in some way, whether it was removing dead or broken branches, structurally pruning, or raising the crown. Pruning trees in the winter is the best practice, as the trees are dormant and the risk of pest problems associated with pruning cuts are minimized, plus the tree has all of the growing season ahead to compartmentalize the wounds. Also the tree is naked in the winter, so it is a lot easier to see the structure of the tree.

Our pruning work focuses on establishing good tree structure and reducing the risk of failures from, for example, co-dominant stems, which are very common in elm trees. Structural pruning is beneficial for several reasons: it helps the tree establish a strong leader, enhances the tree’s appearance and form, and influences the ultimate size of branches.

In the field it is fairly easy to judge what works needs to be done in a tree. We like to say, “hit ‘em up, hit ‘em hard,” when the trees are young. Structural pruning is easier on younger, established trees because it is easier to reach the limbs from a ladder and make the cuts. More importantly, the size of the wounds from the cuts will be smaller, and the tree will be able to seal those wounds quicker. For trees that aren’t established (trees that have been in the ground for less than two years), we only inspect for damaged or broken branches. On older trees our work is limited to how high we can safely reach with our tools from the ladder. Also with larger limbs, sometimes greater than five inches in diameter, the work becomes more dangerous to both the crew and the tree.

Warm weather has made this pruning season really enjoyable, but it may cut our work short. There’s a saying that “pruning is a double-edged sword” — a double-edged saw, I would rather say. Pruning a tree can help or hurt a tree depending on where, when and how the cuts are made. Over the next few days and week we will be carefully observing whether buds are beginning to swell and break. We don’t want to prune during bud break or when the leaves are flushing out. I don’t know if six more weeks of winter are in store, but the groundhog, Punxsutawney Phil, saw his shadow today, so maybe I will still get some of that dreadful cold winter weather. Fingers crossed.

DED symptoms appear in individual branches, turning the leaves yellow or brown and withered. Meanwhile, the disease is spreading through the vascular system of the tree (the way it gets its water), affecting other branches and eventually taking down the whole tree. That can happen in just one season.

American elms in the District have a 5 percent chance of dying because of DED. There are American elms that are resistant to DED, but those cultivars are susceptible toother threats. The best practice is to identify infected branches early and eliminate the offender before the disease has a chance to spread.

If you want more information on identifying and managing DED in your trees, you can read this report by the Department of Agriculture’s Forest Service.

Barry Stahl, NPS Horticulturist, demonstrates a pruning technique.

To help our staff and Citizen Foresters fine-tune their pruning skills, we also partner with the Barry Stahl, Horticulturist with the U.S. National Park Service (NPS) at Daingerfield Island on the George Washington Parkway. The on-site American elm nursery is unique since it provides the NPS with a continuous supply of native elms, as well as disease resistant and historically significant elm cultivars that are not commercially available.

Those lucky enough to get a spot in last Saturday’s pruning workshop learned about the history of American elms in the U.S. and D.C., Dutch elm disease (boo!), proper pruning tools and techniques and much more. Immediately afterward, participants practiced their new and/or strengthened pruning skills on five-year-old American elms grown from seed right at the nursery.

We’ve put together a video montage profiling the workshop (below) and uploaded some great photos onto our Flickr page. Check them both out.

If you would like to learn more about trees, consider registering for one or all of our Citizen Forester-qualifying courses – Trees 101 (Sat., Jan. 21), Stand Up for Trees (Sat., Feb. 4) and Tree Planting (Sat., March 3). Already tree savvy or a Citizen Forester? Think about Trees 201 (Sat., Jan. 28). All classes are free but require advance registration.

We have planted American elms in every ward, restoring historic elm corridors such as Massachusetts Avenue NW and Constitution Avenue NE, as well as street trees in neighborhoods like Brookland and Mount Pleasant.

To help you locate where new American elms are calling home, our savvy Technical Services and Research department mapped them for you. Check it out.

Click on individual points on the map to view Street View or find out the size of the tree (DBH – diameter at breast height). You can zoom and pan the map to explore our planting sites throughout D.C. If you are on a mobile phone or tablet, try a full-screen version of the same map.

This map was created using Google Fusion Tables from data collected at planting sites. Check out other maps on our website.

Want to learn more about American elms? Tune in for our online chat about them today at noon. If you miss the session, the chat will be archived on our website for you to check out at your leisure.

Update:
So we mentioned “over 2,000″ elms planted and as you can see we planted American elms just about everywhere in DC. How does that break down by ward? Here are some additional statistics of American elms planted by ward:

Ward 1: 201
Ward 2: 158
Ward 3: 110
Ward 4: 374
Ward 5: 209
Ward 6: 509
Ward 7: 324
Ward 8: 149
Total: 2,034 American elms planted since 2003 by Casey Trees.

For tomorrow’s Tree Talk Thursday session, we will be discussing American elms. From noon until 1:00 p.m. tomorrow, tune into the live online chat to ask questions and get instant answers from the experts. The chat will feature Jim Woodworth, our Director of Tree Planting. Jim will explain Casey Trees’ American Elm Restoration program, what kinds of elms we plant and lots more about the history of elms in D.C.

Tune in here at noon tomorrow, January 12, to join the chat. If you would like a reminder before the event, enter your email address on the page and you’ll be invited to join when the chat starts.

You can also view our past Tree Talk Thursday chat sessions about choosing an arborist, the pending tree bill and other timely tree topics. Submit questions during the chat or ahead of time by emailing us at treedc@caseytrees.org or tweeting @CaseyTrees. We look forward to seeing you there!

Unfortunately, the pruning class is full, but don’t let that stop you from checking out our calendar and signing up for any of the other open classes currently listed, such as our Trees 201 class on January 28th geared towards Citizen Forester, Project Organizers and others who want to learn more about tree identification.

It’s January, so we are again celebrating the American elm. The American elm is one of the oldest continuous residents of Washington, D.C. and is a hardy street tree that provides shade and beauty for many neighborhoods in our city. We work to restore these trees because of the challenges they have faced, both in our city and throughout the nation. From Barracks Row to quiet residential streets to the National Mall, American elms help make D.C. the City of Trees.

Starting in December and continuing through this month, we are planting 200 American elms through our American Elm Restoration program. We will focus on planting disease-tolerant variants of the tree along historic elm corridors where the trees once thrived. Every winter we work with the Urban Forestry Administration to plant over 1,850 of the trees since the program’s inception in 2003.

In celebration of this special tree of the month, we will share stories and information about the American elm throughout January — stay tuned! Also, if you’d like to learn more about our American Elm Restoration program, visit our website.

• Fungal infection – Ophiostoma novo-ulmi and O. ulmi
• First described in 1921 in Holland and spread to the United States by 1930. Reached Washington, DC mid-20th century.
• Transmitted primarily by the native and European species of the elm bark beetle that feed on elms. Can also spread from tree to tree when roots cross and become grafted together.
• American Elm street trees can have rates of death higher than 5% annually. DC lost 70% of its street elms between 1959 to 2002 when Casey Trees did its first city-wide tree inventory.

A withered DED-infected branch alongside healthy branches.

Leaves on affected individual branches shrivel and brown. Symptoms commonly are observed in early summer, but  can be seen at other times of the year. Other elms are susceptible to DED, but the American Elm is especially vulnerable, unless it is a cultivar that has significant resistance (but no immunity). The disease is spread by beetles that carry fungal spores from the diseased elms to healthy elms. The beetles movement and the threat of spreading from a DED-infected tree to neighboring trees means that an entire street of elms can be at risk if there is even one diseased tree in the area. 

The virulence of DED necessitates an intensive management strategy that requires infected trees to be identified and removed as quickly as possible. Insecticide or fungicide methods are also used, but may be expensive. Planting resistant cultivars is a good strategy, but even those trees may be susceptible to elm yellows. Often only one branch is initially infected. In such cases, an arborist can quickly undertake a sanitation pruning to remove a diseased limb. Without intensive management, DED is fatal for an American Elm. 

Phloem Necrosis (Elm Yellows)

• Viral infection – Morsus ulmi
• Trees usually die within a year of symptoms.
• Transmitted by the whitebanded elm leafhopper, and also through root grafts.

Healthy elm (left), elm yellows (right). Photo credit: Wayne A. Sinclair, Cornell University, bugwood.org

• Bacterial infection – Xylella fastidiosa
• The disease clogs the xylem, impeding water transportation through the tree which prevents water from reaching the leaves.
• Causes annual summer/fall symptoms of browning (scorched) edges of leaves, creating a “halo” effect.
• Can be transmitted by a xylem-feeding leafhopper.
• Trees decline over many years rather than dying immediately.

• Fungal infection – Verticillium albo-atrum
• Carried through the roots of elms, transmitted through the soil.
• Dieback symptoms are similar to DED – leaves begin to wilt on individual infected branches.