Host an Event Volunteer Join Tickets

Support the plant database you love!

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?

Share

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
Not Yet Rated

Friday - June 24, 2011

From: Round Rock, TX
Region: Southwest
Topic: Turf
Title: Roots of live oak in lawn from Round Rock TX
Answered by: Barbara Medford

QUESTION:

I live on a cul-de-sac and have a small triangle shape yard. There is a large live oak in the middle of the yard. I am concerned because large bark covered roots have emerged on two sides of the tree. The roots are so large, I am unable to use my lawn mower around them. Is my tree in trouble? Should I forego grass and landscape around the roots? Thank you.

ANSWER:

Yep, that's what oak roots do. Your tree is not in trouble, but your lawn probably is, and we can't guarantee that planting anything else under there will be successful, either.

Given the choice between having great trees and having ground cover under them, we would vote for the trees every time. And it's necessary to remember that most tree roots occur in the upper 12" of soil, and may extend three times the dripline of the tree. Oak roots also form a mat beneath the soil, which discourages any other plant. Planting within the dripline can damage the roots of the tree, and the understory plant probably doesn't have a chance of competing anyway. The Lady Bird Johnson Wildflower Center recommends only plants native to North America and to the area in which they are being grown, as these are adapted by millions of years of experience to the soil, annual rainfall and temperatures of that area. We still can't guarantee that any plants you might choose would even survive beneath your trees, and you may decide to simply cover the bare ground with a good quality shredded hardwood mulch. This will have to be replenished from time to time, but as it decomposes, it will add nutrients to the soil, and improve the soil texture, as well as protecting the tree roots from heat and cold.

There is also the problem of the shade the tree casts. We consider full sun to be 6 or more hours of sun a day, part shade 2 to 6 hours of sun, and shade less than 2 hours of sun a day. Finally, there is the question of allelopathy. Various studies have demonstrated that oaks can have allelopathic affects on surrounding plants. Allelopathy is the production of plant inhibiting chemicals by one plant to regulate the growth of others in its vicinity. One important group of chemicals produced by oaks is tannins. They are produced in leaves and litter and also directly by root systems in soil. Tannins are inhibitory to many organisms. Salicylic acid and other organic acids are also produced by oaks and are toxic to other plants. Allelopathy is species specific for the oak in question and the species that is inhibited.

So, bottom line, no, don't try to mow over those roots. In fact, keep machinery away from your tree, remembering that damage to the bark can cause sap to leak out, which is an invitation to the nitulidid beetle, a carrier of the oak wilt fungus.

 

 

More Turf Questions

Short native turf grass for Texas lawn
January 31, 2009 - I would like a native grass mix that doesn't get too tall. It is mostly sun with afternoon shade. Mowing wouldn't be a problem, but not necessary. The soil is pretty good but shallow.I hate the ber...
view the full question and answer

Native replacement for non-native Bermudagrass in Leander TX
October 16, 2011 - We have Bermuda grass. Large patches have died due to the drought and our yard has been taken over by weeds and St. Augustine grass whose seeds must have blown in. Even when the grass was in great con...
view the full question and answer

Drought-resistant and grub-resistant grass for Smithville TX
October 02, 2012 - I want a drought resistant grass for a sunny area that is also resistant to grubs. I have lots of grubs but want a healthy soil of good microbes. Any ideas? Zoysia, Buffalo? I noticed that Tech Turf r...
view the full question and answer

Substitute for Habiturf in Fullerton, CA
March 27, 2015 - Will habiturf grow/thrive in 92835 zip code? I think Im on 10a or 10b hardiness. I have clay soil. Thanks
view the full question and answer

Native grasses for lawn in Michigan
June 14, 2009 - I want to plant a lawn of grasses that are native to Michigan specifically. My soil is a little sandy in some spots and is moderately moist. I have been researching on the internet and I *think* tha...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.