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

Agave americana/Century Plant care and life cycle.
June 10, 2009 - How often do century plants bloom? Do you have info on how to care for them?
view the full question and answer

Possibly non-native succulent identification
March 27, 2008 - My mother has a plant that grows on a stalk, 2.5' tall, leaves are about 4-5" on the mature plant. The leaves are scalloped on the edges and seeds grown in the scallops & fall off and make new plan...
view the full question and answer

Problems with claret cup cactus in Austin
April 07, 2012 - I have a claret cup cactus in a terra-cotta pot that bloomed beautifully a few years ago but hasn't since. This year, it set about a dozen buds and looked poised to bloom like crazy, but two weeks la...
view the full question and answer

Bloom stalks on agave plants
September 26, 2007 - Hi, We have Agave plants in our garden for years. But in the past few weeks, we noticed a giant asparagus looking thing growing out in the middle of the plants. We don't know what it is, but every d...
view the full question and answer

How do cacti stay in ground
February 25, 2005 - How do cacti stay in ground? I know that flowers stay in the ground by their roots but what about cacti?
view the full question and answer

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