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

Monday - May 11, 2009

From: Kyle, TX
Region: Southwest
Topic: Rain Gardens
Title: Expanding clay soils near rain garden
Answered by: Nan Hampton and Chris Caran


I want to put a rain garden in my yard in central TX (Kyle). My subdivision architectural review committee expressed concerns about the expansive clay soils becoming saturated and possibly shortening the anticipated lifespan of a sidewalk and alleyway near by. How do I find information about setback distances for clay soils? I have found that most rain garden plans recommend 10' from foundations, but no comment or mention about distances form sidewalks and alleyways. I found that in Seattle they have rain gardens in the planting strip between the roadway and sidewalk without concern for damage to road or sidewalk. How or where can I get help with this concern? Thanks


First of all, and I'm sure you know this, Seattle soils are not like Kyle soils.  I've thought about your question a great deal and, although I wasn't able to find any exact recommendations for distances from sidewalks or streets,  I did get some insights from consulting a geologist friend who knows a lot about the expansive clay soils of Central Texas.  This is a summary of what he says about your problem:  When the weather has been dry, these expansive clay soils shrink and become permeable with small channels running through them much like the honeycomb limestone of the area.  When it rains, the water runs through them vertically until they absorb enough to expand and become impermeable.  They expand vertically as well as horizontally.  When they absorb enough water to become impermeable, the water runs off the surface.   The soil can't expand further at this point.  The water you catch in your rain garden pond is going to permeate the clay soils underneath it until they become saturated and almost impermeable.  Then, the pond will hold the water until it evaporates or seeps slowly down into the ground.  The soils under and perhaps adjacent to the rain garden WILL expand considerably once they are wet, so any structures (e.g., pipelines, walkways, etc.) in the immediate proximity of the garden can be expected to shift.  The adjoining clay soil in the yard is also going to expand just from the rain that falls on it and the soils near the sidewalk will expand after a rain regardless of whether there is a rain garden nearby or not.  If 10' is the recommendation for foundations, that would seem an adequate distance for sidewalks as well.

More Rain Gardens Questions

Raingardens in Indiana
May 09, 2012 - I need to have annual native plants to add to a demonstration rain garden to fill in while we wait for the perennial plants to mature. The only plant I can think of is annual phlox. Do you have any ...
view the full question and answer

Bioswale for Indianapolis
September 13, 2009 - The city of Indianapolis has a very historic Central Canal, which was built in the 1830s. Due to erosion, the parent company of Indianapolis Water, Veolia, has proposed covering the banks with a type ...
view the full question and answer

Rain garden plants for DC
March 23, 2011 - Please recommend deep-rooted, native, perennial plants, 1-3 feet high, for an area that is moist and gets approximately 3 hours of day of afternoon sun. During rain storms this garden is in a low area...
view the full question and answer

Plants for Bioswale in Illinois
November 30, 2009 - I have a 300ft by 15 ft bioswale in Aurora, Illinois. What plants would be best used? Is there a percentage of each plant to take into consideration?
view the full question and answer

Rain garden plants for Central Texas
February 06, 2014 - Do you have a list of rain garden plants for Central Texas?
view the full question and answer

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