En Español

Q. Who is Mr. Smarty Plants?

A: There are those who suspect Wildflower Center volunteers are the culpable and capable culprits. Yet, others think staff members play some, albeit small, role. You can torture us with your plant questions, but we will never reveal the Green Guru's secret identity.

Help us grow by giving to the Plant Database Fund or by becoming a member

Did you know you can access the Native Plant Information Network with your web-enabled smartphone?


Ask Mr. Smarty Plants

Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

Search Smarty Plants
See a list of all Smarty Plants questions

Please forgive us, but Mr. Smarty Plants has been overwhelmed by a flood of mail and must take a break for awhile to catch up. We hope to be accepting new questions again soon. Thank you!

Need help with plant identification, visit the plant identification page.

rate this answer
17 ratings

Sunday - September 14, 2008

From: San Antonio, TX
Region: Southwest
Topic: Diseases and Disorders, Pruning, Trees
Title: Pruning mature cedar elm trees in San Antonio
Answered by: Barbara Medford


When is the right time to prune my several mature cedar elm trees? I'm in San Antonio, and they have never been trimmed in the 55 years we have lived in this home. I have several that are at least 70 ft tall and they need cleaning up. I wouldn't want to harm them, though.


Ulmus crassifolia (cedar elm) is a native North American deciduous tree which reach 50 to 90 feet in height with a spread of 40 to 60 feet. It would be a low maintenance shade and street tree except for its thin drooping branches which are somewhat susceptible to breakage at the crotches of major limbs. Some of this could be avoided by maintaining a regular pruning and training program in the early years after transplanting. For more information, see this USDA Forest Service website on Cedar Elm.Your elms have already had a pretty good life span, at 55+ years, and are at a height to be expected at their age. They have a fairly long life span, perhaps 150 to 300 years. So, at first glance, we could say your elms have been doing just fine, and need no trimming, etc.

However, the main drawback to the elm is Dutch elm disease. Dutch elm disease was first discovered in Ohio in 1930. Spores of the disease are carried on the bodies of elm bark beetles and are deposited in tree wounds. The beetles, perhaps introduced accidentally from Asia, attacked trees that had not had a chance to develop a resistance to the disease over time. It is caused by a fungus transmitted by two species of bark beetles.

Avoid pruning from April to August. The elm bark beetle is attracted to freshly cut elm and is most active during this period. Prune dead or dying branches from Fall to late Winter. We would urge you to engage a licensed arborist, for several reasons. They will be aware of the potential problems for the elm tree, and know when is the appropriate time for pruning. Also, they will have the equipment and expertise for dealing with such a large tree. Please don't climb up your trees with a chain saw. You will possibly damage a whole lot more than the tree.

Ulmus crassifolia

Ulmus crassifolia

Ulmus crassifolia

Ulmus crassifolia



More Diseases and Disorders Questions

Problem with American Beautyberry in Houston.
July 02, 2014 - My American Beautyberry is dying one branch at a time. The entire plant looks great, now flowering and starting to put out berries. Then one or two branches will completely die. Trim those off, wi...
view the full question and answer

Watering Houseplants with Soapy Water
August 22, 2011 - I accidentally watered my house plants with a container that had a some dishsoap in it. Will they be okay? One of the plants is a 20yr old cactus, with small roots.
view the full question and answer

Black Sooty Mold on Bay Tree
February 25, 2013 - I have a large bay tree and all the leaves are covered with a black mold-like substance on the top part of the leaf. Under each leaf are some black/brown spots. I have washed the leaves with soap and ...
view the full question and answer

Mildew on phlox paniculata from Morrisville PA
May 30, 2014 - My Phlox paniculata, all 7, have powdery mildew. I read about using NEEM to combat the mildew. NEEM is organic but the bottle says it is also an insecticide. The phlox are near my milkweed and gold...
view the full question and answer

Stressed Ashe juniper is dropping needles
May 07, 2015 - We have a large Ashe juniper tree in our backyard, at least 20 ft tall. This past winter/spring, several limbs have died and it's dropped a ton of leaves (clumps of "needles" really). Is it slowly ...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2016 Lady Bird Johnson Wildflower Center