April 1, 2000

Question: Is there such a thing as hydrophobic sand? On my septic field after a good and prolonged sprinkling, the soil is only wet to a depth of ˝ inch. Almost no absorption. The underlying sand is totally dry. 
- Robert Levering, Sanibel

Answer: Yes, there is such a thing as hydrophobic soil. Soil microorganisms are thought to be responsible for the inability of some soils to absorb water. Perhaps the most significant contribution of soil microorganisms is process of organic matter decomposition. However, as part of this process, some soil microbes deposit a residue that coat sand particles. Upon drying, the residue resist the absorption of water. Consequently, there are areas in some landscapes that will routinely fail to absorb sufficient water. The organisms responsible for hydrophobic soils are concentrated just below the soil surface and to a depth of about 12 inches. Outside that zone, water is generally easily absorbed by the soil. Hydrophobic soils is a phenomenon of native and cultivated soils. 

There are no products available that will reduce the hydrophobic nature of affected soils. However, polymers are sometimes incorporated into soil to help retain moisture. The polymers are capable of absorbing great amounts of water but have no effect on eliminating the hydrophobic residues deposited by soil microorganisms. These polymers are not easily found. The use of mulch, or the incorporation of organic matter into soil, are ways to combat the effects of hydrophobic soils. 

Stephen Brown is a horticulture agent with the Lee County Extension. To submit questions call the horticulture desk at 461-7504 between 9 a.m. and 4 p.m. or via e-mail at shb@gnv.ifas.ufl.edu.  Listen to the ‘Garden Show’ at 8 a.m. on 1200-AM WINK/WNOG.

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