I Am Not an Arborist…

…. but I sometimes, cautiously, play one at home. So, of course, now comes the disclaimer: Pruning trees badly can have long-term, negative consequences and so it is highly recommended that you consult a certified arborist. Anyone who suggests extensive pruning (more than 15 – 20%) or, heaven forbid, topping should be dismissed.

In the summer of 2007, I hired Chuck Owen to prune my mature coast live oak. It was expensive and worth every penny of it. The tree, though healthy, had never been pruned during the eleven years that we lived in our house, and had accumulated a lot of dead wood. Chuck’s crew worked on it for an entire day and when it was finished you could not tell it had been pruned. The dead wood was gone and the tree looked clean and healthy but not shorn. Three years later it still looks great. There wasn’t a flush of new growth after the pruning because it was done properly.

The skilled crew was supervised by a certified arborist. A surprisingly large amount of dead wood and crossed branches were removed from the tree.

Chuck and Master Arborist, Susan Sims, will be giving a free oak tree pruning workshop at Rancho Santa Botanic Garden this weekend. I just signed up for it myself. If you have trees and intend to do any pruning, I highly recommend that you attend a class offered by a qualified arborist.

So, why post about pruning oaks before the workshop? Well the reason is that I jumped the gun and did some minor pruning last week on the oaks that I planted five years ago in the parkway. It is best to prune evergreen oaks in late summer to fall, when they are dormant. For the past five years I have resisted pruning these young trees except for branches that extended out into the street or sidewalk posing a hazard to pedestrians or cars. By this year, the lower branches, so important to the early development of trees, had gotten thick and tangled, extending out to the walk and street. And so finally I decided it was time to remove some of these low growing branches. I also looked for branches that were crossed, or had narrow crotches and removed these as well.

Coast live oaks in parkway before pruning. Lower branches were growing into sidewalk and street.

I planted these three coast live oaks – after getting city approval – in my 75 foot long parkway in December 2005. The young trees had not been lollipopped (a practice of removing lower juvenile branches and cutting upper branches to give a young tree a shape that mimics a mature tree – actually it mimics a child’s drawing of a tree). They were nice looking specimens grown by Tree of Life Nursery.

One of three coast live oaks (Quercus agrifolia) shown at time of planting, December 2005 (left), and now, August 2010 (right).

The trees were not staked when planted, and as a consequence they developed a “beefy” caliper with a nice flair (widening) at the base. Restricting the movement of young trees by tightly staking them reduces the development of a thick caliper that widens at the base, resulting in less stable trees.

Base of one of the oaks shows bark growth cracks, indicating healthy growth.

I know I should have waited until after the workshop but I actually hadn’t planned on attending. So armed with knowledge picked up from previous classes and reading material, I approached the trees. The first thing I did was select the branches that needed to go. This isn’t simple, and again I would recommend attending workshops or classes before doing it. Once the branches are selected, be sure to cut above the branch collar so that the tissue can continue to grow over the wound, healing the cut. The cut should be level with the collar edge. If you leave a small stump it will grow leaves or just die, neither of which is healthy. All cuts should be made with sharp, clean, and appropriate tools. (See the references listed below for more tips on pruning.)

Cut made above branch collar.

After pruning of lower branches.

This post provides a quick and dirty description on my experiences with oak tree selection, care and pruning. There is much, much more to this, but to summarize:

1. Select healthy specimens that have juvenile branches in place. Avoid plants with long, thin trunks that do not have lower branches (lollipop-shaped plants). Make sure that the tree has healthy roots that have not become girdled (wrapped around) in the pot, and that it does not show any other signs of disease.
2. Only stake trees that require extra support. Movement of the young tree is important for the development of a thick trunk with a strong, anchoring root structure. Remove stakes as soon as possible. And never leave a nursery stake (stake that runs along the trunk) in place.
3. Allow the tree to grow for several years before thinning or removing juvenile branches.
4. Prune at the right time of year – July and August for coast live oaks.
5. Prune properly using standard arboriculture procedures. Educate yourself on how to care for and prune trees.
6. Never, ever, ever top a tree, or hire someone who would do such a thing!

For more information on oak tree care, check out the California Oaks website (a project of the California Wildlife Foundation). The International Arborist Society has excellent information on selecting, pruning young and mature trees, and general tree care: Trees are Good. And finally, the California Oak Mortality Task Force has an excellent booklet on oak tree care, Living Among the Oaks.

A few other non-web resources on oaks trees follow:
Bush, Lisa and Rocky Thompson. 1989. Acorn to Oak – A Guide to Planting and Establishing Native Oaks. Windsor, CA: Circuit Rider Productions, Inc.
Booklet with practical information on planting oaks.

California Native Plant Society, Oak Hardwood Committee. 1989. Oak Action Kit: Resources for Preservation and Conservation of Oak Habitats. Sacramento, CA: CNPS.

CNPS, 1990. Fremontia – Year of the Oak.
Issue of Fremontia dedicated to oaks.

Fuentes, Lorrae and Bart O’Brien. 1998. Maintaining An Existing Native Oak in the Home Landscape, pp. 30-32. In California Oaks Trail Guide. Claremont, CA: Rancho Santa Ana Botanic Garden.
Three pages with do’s and don’ts for coast live oak.

McCreary, Douglas. 1990. Native Oaks- the Next Generation. In Fremontia, 7/90, pp.44-47.

Pavlik, Bruce M., Pamela C. Muick, Sharon Johnson and Marjorie Popper. 1992. Oaks of California. Los Olivos, CA: Cachuma Press, Inc. and California Oak Foundation.

Hope to see you at Rancho on Saturday.