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Wednesday - July 13, 2011

From: Austin, TX
Region: Southwest
Topic: Compost and Mulch, Watering
Title: Possibility of hydrophobic soil in Austin, TX.
Answered by: Jimmy Mills

QUESTION:

I believe I have an area in my garden with “hydrophobic soil”: no matter how much or how slowly I water, it just beads up and rolls off and the soil beneath remains cement dry and powdery. In my reading on the internet, it suggests using a very dilute solution of soapy water (1 tsp soap to 5 gallons of water), to decrease the surface tension, but it seems this is only a temporary fix for the next watering. I also read that bagged bark mulches can be the cause (I have been using bagged native Texas bark for several years. What are your thoughts?

ANSWER:

I must admit that I hadn’t heard of “hydrophobic soil” until I read your question and started looking on the web for an answer. How large an area are we looking at? This may influence the remedy that you choose.

Lets start by looking at soil in general. This article from Bachman’s Gardens gives a good overview of the nature of soil, its components, and the role of soil texture (ie particle sizes) in determining its water holding capacity. Generally, sandy soils allow more percolation than soils with finer particles.

This link from the University of Florida answers the question that I had:”What is hydrophobic soil?, suggests a possible cause, and offers mulching as a remedy.

A link from treesfoundation.org (starting with the third paragraph) describes how hydrophobic soils can be the result of wildfires.

One possible remedy for hydrophobic soils is the use of non-ionic surfactants on the soil (University of North Carolina).

This forum from Gardenweb.com has comments from those who prefer the use of surfactants (soapy water) as well as those who propose changing the texture of the soil eg. adding mulch or compost and spading in the organic material.

I am partial to the latter, depending on the size of your garden plot.