En EspaŅol

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
Can't find the answer in our existing FAQs, submit a question to Mr. Smarty Plants.
Need help with plant identification, visit the plant identification page.
rate this answer
Not Yet Rated

Wednesday - December 02, 2009

From: Marble Falls, TX
Region: Southwest
Topic: Cacti and Succulents
Title: Potted crown of thorns cactus cold tolerance in Marble Falls, TX
Answered by: Barbara Medford


I have a large potted crown-of-thorns cactus. Can it remain outside this winter in the Texas Hill Country?


When we originally received this question, we went to our Native Plant Database and found Koeberlinia spinosa (crown of thorns), which grows natively in far South Texas and the Big Bend area, where temperatures are warmer than they are in Central Texas; however, this plant is known to be hardy to 0 deg. F. So, we replied that we thought the potted plant would be all right outside. Turns out we let the common name curse keep us from finding the plant actually referred to in the question. This old-fashioned houseplant, Euphorbia milii, crown of thorns, is more likely the plant about which the inquiry was sent. 

The Lady Bird Johnson Wildflower Center is dedicated to the use, care and propagation of plants native not only to North America but to the area in which it is being grown. This puts this native of Madagascar our of our realm of expertise. We can tell you that while we said the Koeberlinia spinosa could be wintered over outside in a pot in the Hill Country of Texas, we find that the Euphorbia milii is only hardy from Zones 9b to 11. Central Texas is generally Zone 8a. The plant itself would be threatened by a hard frost in this area, and certainly a plant with its roots exposed in a pot would be even more likely to be damaged by cold weather. Euphorbia milii should be treated as an indoor potted plant over the winter. Here is more information on this plant from Floridata and pictures from Google

One further note: neither the Koeberlinia spinosa nor the Euphorbia milii are cacti. Koeberlinia spinosa is a member of the Capparaceae or Caper family, while Euphorbia milii is a member of the Euphorbiaceae or Spurge family.


More Cacti and Succulents Questions

20 years to bloom
May 02, 2007 - My girlfriend and i have come up with an interesting question, we were wondering if there is a plant in existance that takes over 20 years to bloom, and how many different kinds (if any) there are? We...
view the full question and answer

Trimming of dead foliage on trunks of yucca in California
December 21, 2008 - There is a Yucca plant in the back yard. I want to know how to get the old foliage that has died off of the trunks, it looks kind of ragged. The foliage is about three feet from the green. Can you ...
view the full question and answer

Skin Reaction form Cochineal on Prickly Pear
February 16, 2015 - I have severe burning and peeling skin on pads of fingers after touching "white stuff" on a prickly pear. White stuff tuned purple then burned skin even after washing hands. Skin has been cracking a...
view the full question and answer

Damage to yucca in San Marcos TX
October 18, 2010 - Dear Mr. Smarty Plants, thank you for helping me with my buffalo grass is San Marcos TX back in the spring, my lawn is gorgeous thanks to you! I really need your help as someone sabotaged my beauti...
view the full question and answer

Need help with yucca palm in New York City, NY.
November 10, 2011 - I have had my yucca palm plant for almost 10 years. The bark has started to peel off although leaves seem fine. The second smaller separate yucca plant has half its bark and trunk gone. I can't see a...
view the full question and answer

Support the Wildflower Center by Donating Online or Becoming a Member today.
© 2015 Lady Bird Johnson Wildflower Center