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Jen Kettell’s Practical Pruning Advice

by Mary Jasch

Horticulturist Jennifer Kettell started at Harvard University’s Arnold Arboretum as an intern 10 years ago. Now her job encompasses the care of 22 acres of linden, horsechestnut, hickory, dwarf conifer, juniper and multiple mixed collections.

During January, February and March Kettell prunes trees, shrubs and woody vines, some over 110 years old, in the Arboretum.

Kettell likes to prune most woody plants in late winter/early spring because:
1. you can see what you’re doing before the leaves get in the way
2. plants have stored energy
3. there is no insect or disease activity at this time

A few plants Kettell has in her pruner sights right now are large yews, viburnum, Lonicera sempervirens, wisteria, hollies, and the larger hybrid clematis (every few years take a bit more off until you cut it down to two feet). Although any time is a good time to remove dead or diseased branches, Kettell recommends pruning after flowering for redbud, magnolia and cherry. For more tender shrubs such as roses on which some winter die-back is expected, she waits until they start to leaf out to determine the damage.

Trumpet Vine: If you have an older one that’s out of control, cut it back hard. You don’t have to worry about how much you take off.

“With any plant you want to prune, ‘how’ is far more important than ‘when’,” says Kettell who graduated from U of Massachusetts, Amherst with a BS in Psychology so she understands where trees are coming from. Kettell worked in psychology for nearly 10 years before interning at the Arnold Arboretum.

Jen Kettell's recommended strategy:
- Identify the plant.
- Determine its natural habitat.
- Help guide it (by pruning) to look like it’s in its natural habitat
- Understand that your yard is different than the forest

Example: American beech (Fagus grandiflora)
In its natural forest habitat surrounded by other trees, a beech tree receives less light, mostly on the crown. It has fewer branches, fewer buds and competes with other trees for nutrients, sun and water. It becomes tall and straight. In a yard, every bud of a beech tree has access to sun, nutrients and water. This results in a very dense plant.

“Your job as pruner/caretaker of a beech tree in your yard is to decrease the crown and remove rubbing branches. Your job is to thin out the tree with an intelligence about what it’s supposed to look like,” says Kettell. “The plants themselves are our teachers. If you look at a grove of beeches in the woods, all of the seedlings are close together, competing with each other. Pruning happens over a long period of time. Branches get shaded out and fall off exactly where they should. In our yards we can’t leave the trees alone because we are growing them in a landscape.”

How to Make the Cut:
Cut just outside of the branch collar, the swollen area where the branch meets the main trunk. The collar contains plant chemicals that ward off decay while it’s closing over the cut, like a wound scabbing over on your finger. Studies show that there is a big difference in the amount of decay over time with a flush cut versus a proper cut just outside the collar.

“You always want to cut back to a branch collar," Kettell advises. "If not, you’re not doing it properly. Some shrubs, like spiraea or hydrangea, can be headed back; that is, cut back to a bud/leaf, but never with trees. When pruning, take a step back 10 to 15 feet and look at what you’re doing. You don’t want to take off too much. When pruning, take a step back 10 to 15 feet and look at what you’re doing. You don’t want to take off too much.”

Jen Kettell’s arsenal:
- E-Z-Ject, a long lance-like pole with chambers full of shot-gun-like shells of herbicide
- Trees of the Northern United States and Canada by John Laird Farrar (black and white silhouettes)
- Felco bypass pruners (no anvil pruners that smash branches)
- 12-inch saw with tri-cut blade (three surfaces on each tooth)
- Silky Gomtaro saw with straight blade for shrubs and small trees
- Silly Zubat saw with curved blade, with more torque they’re best for large shrubs and yews with dense wood
- ARS small bonsai saw with teeth that go to tip for small, tight shrubs like dwarf lilacs and azaleas
- chainsaw for large branches on trees or very large shrubs
- leather safety gloves “Cuts can be pretty deep and pretty bloody. You want to avoid that.”
- hiking boots

After the pruning, Kettell kicks off spring by digging, ball & burlapping and planting young trees. She is responsible for pest and disease management, mowing, edging shrub beds, mulching, training summer interns, weeding, pruning, leaf pickup, mulching-in and snow removal.

As if that’s not enough or near impossible, Kettell says: “I am an ISA (International Society of Arboriculture) Certified Arborist and serve on the Executive Board of Directors for the New England Chapter. I also serve on the Landscape Advisory Committee for the Esplanade Association, the Advisory Committee of the Norfolk Agricultural High School, and own my own business in horticulture education and consulting. I keep busy.”

Although Kettell works full-time at the Arnold Arboretum, she runs her own business: Jen Kettell, Horticulture Education and Consulting. “My main service is home pruning classes, where I teach customized lessons to homeowners in their own yards, on their own plants.”

Her last advice: Take a chainsaw safety class if you have any intention of using a chainsaw. The Arnold Arboretum teaches one. The New York/ New Jersey Trail Conference teaches USFS Chainsaw Safety Certification and you don’t need to own a chainsaw. Check with other public gardens and arboreta, trail organizations and state forest services. If you don’t see it, ask.

- Dan Tilton, National Safety Director for Tilton Equipment Company
- Arnold Arboretum: www.arboretum.harvard.edu
** All photos Courtesy Jen Kettell

Jen Kettell, Horticulture Education and Consulting: www.jenkettell.com

Upcoming Classes at Arnold Arboretum: February 23-Dwarf Conifer and Juniper Collections via Snowshoes; March 16-Pruning Shrubs

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