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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.

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Ask Mr. Smarty Plants is a free service provided by the staff and volunteers at the Lady Bird Johnson Wildflower Center.

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Tuesday - May 15, 2007

From: Austin, TX
Region: Southwest
Topic: Cacti and Succulents
Title: Root depth of opuntia
Answered by: Nan Hampton

QUESTION:

What can you tell me about the depth of roots of the opuntia? Does it vary with different varieties or is there formula to estimate the depth according to the mature size or to the culture - garden soil - wet or dry - etc ?

ANSWER:

As far as Mr. Smarty Plants knows, there is no magic formula to determine the depth of the roots of Opuntia spp. In general, the Opuntia cactus have tap roots with extensive shallow lateral roots. The size of the tap root and the lateral root expanse has to be correlated, to some extent, with the plant's age and size; however, environmental factors, such as abundance of water, soil temperatures, and CO2 concentration, also have a large effect on tap root depth and lateral root extension. For instance, a study of certain Opuntia species naturalized in Africa has shown that water stress increases the length of the tap root and reduces the size of lateral roots. In Opuntia ficus-indica increasing soil temperatures and CO2 concentrations cause the lengthening of tap roots.

You can read more about cactus survival strategies.

 

 

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