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
3 ratings

Saturday - October 25, 2008

From: Austin, TX
Region: Southwest
Topic: Invasive Plants, Non-Natives
Title: Getting rid of giant ragweed in Austin
Answered by: Barbara Medford


How can I get rid of a large field of giant ragweed? Part of the site is a steep slope, which is difficult to mow. I want to encourage native grasses but they are crowded out by the ragweed.


The best information we could get on Ambrosia trifida var. texana (Texan great ragweed) after doing some research is to allow perennial plants to crowd out this annual. Yeah, right.

So, here's the plan. Get them before they go to seed. And really get them-either cut off the seeding part or pull out the whole things. They're blooming now (thus all the allergies all over town), and once they've bloomed, they set seed. Birds love the rich, oily seeds for winter food, so you're going to make some birds unhappy, but if you don't want a fresh field of new Giant Ragweed next year, those plants have got to go before the seeds ripen. This is not to say they won't come back, because the birds are going to pick up seeds in the field next to yours, and deposit them for you. But if you can slow it down to the point that you recognize them when they're young and yank them out then, long before they even produce the flowers and pollen and sneezes, then you're at least gaining. 

Most of the native grasses you are interested in are, indeed, perennials and will, given half a chance, begin to dominate the area, but the ragweed, although annual, is just so numerous that it can shade out the perennial grasses and seriously damage their growth. So, there you have it - you're going to have to do it the hard way, and mid-October is a real good time to start. If you wait until they die back in cold weather, they will have already deposited millions of seeds in the ground, and be all ready to go next year.

Ambrosia trifida var. texana

Ambrosia trifida var. texana

Ambrosia trifida var. texana

Ambrosia trifida var. texana



More Invasive Plants Questions

Is non-native cotoneaster poisonous to goats from Eureka CA
August 19, 2011 - I have heard that cotoneaster is poisonous to goats and other animals. We are trying to get rid of it in our yard, but I was hoping we could use goats to eat it back. What are our options in removin...
view the full question and answer

Request for native grasses from Hillsboro TX
August 04, 2012 - P.S. I forgot to mention one very important fact: my neighbor specifically asked for "native grass" recommendations. He thought he was getting a native grass recommendation.
view the full question and answer

Invasive mandevilla from Chula Vista CA
December 10, 2012 - How can I rid my yard of mandevilla that has invaded from my neighbor's yard?
view the full question and answer

Destroying seeds of Chinaberry tree
October 23, 2007 - I have a "chinaberry" tree in my yard, and while I understand that it is an invasive plant to Texas, I was hoping to save the large mature tree. As an effort to be more responsible I have been coll...
view the full question and answer

Looking for non-native Chinese Pistache tree
April 23, 2015 - Where in the Austin area would be a good place to find a nice sized Chinese Pistache to plant in my yard?
view the full question and answer

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