Native Plants

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

1 rating

Sunday - September 28, 2008

From: Iredell, TX
Region: Southwest
Topic: Pruning, Trees
Title: Pruning native Senna lindheimeriana
Answered by: Barbara Medford

QUESTION:

I asked a question about pruning a Texas Senna tree. The Texas Senna I have is either a S. wislizenii or a S.lindheimeriana. It is a beautiful tree that I purchased at a Texas Native Plant nursery. Like I said in my previous email, it is about 7 to 8 feet tall and and about 7 feet across. It has small green leaves and is very bushy and full. My question was how and when do I prune it. Can you please give me some information on this?

ANSWER:

Oops, sorry, you're absolutely correct. Our mistake was to look for the "Texas Senna" in our Native Plant Database, and it wasn't found under that name. The "Texas Senna" we did find was a non-native. This is the problem we run into when retailers name their plants without regard to botanical names. Fortunately, you apparently got (and saved) a label with the proper botanical name.

Senna lindheimeriana (velvet leaf senna) is a tender perennial and considered a sub-tropical herbaceous plant. Senna wislizeni (Wislizenus' senna), on the other hand, is referred to as "shrubby", has thorns, and can apparently take lower temperatures.

We did not find any pruning instructions for either plant; however, we did learn that in colder temperatures, Senna lindheimeriana (velvet leaf senna) will die back, but will come back from the roots. For that reason, we would suggest that you let it run through its blooming season (apparently October is the end), and then trim it back pretty thoroughly. When we prune a plant like that, we always leave stalks sticking up 8 to 10 inches, just so we'll know where it is. If you are expecting some pretty cold weather, it would be a good idea to mulch the roots. The plant should begin to come back from the roots in Spring, and will probably grow bigger and more lush for having been trimmed back.

If you believe that what you have is Senna wislizeni (Wislizenus' senna), we would still recommend pretty good pruning, but maybe not down as low. And, in fact, you might want to wait until late Winter, when you don't expect any more hard freezes, to do that pruning. If you prune it too soon, and there is a hard freeze, it could damage new growth starting to emerge.

From the Image Gallery

Lindheimer's senna
Senna lindheimeriana

Canyon senna
Senna wislizeni