Issue: March 29, 2008

How does our soil lock-up minerals?


I keep hearing that our soil is very alkaline, that it has a high pH, and that this "locks up the minerals in the soil" and keeps them unavailable to our plants. This situation happens in all deserts.

Can you explain how desert soil becomes alkaline, how the pH is affected by desert conditions, what "minerals locked up in our soil" means, and how a more neutral pH can make minerals and other nutrients more available to our plants? This is such a mystery to me!

Siri-G. K.


This is a topic that cannot be thoroughly covered in the space allotted to a newspaper column, but it is a very good questions and important to understanding gardening in the Southwestern U.S. and other arid regions. I will answer it to at least initiate your understanding, but for a more through understanding I would recommend that you look for a course in soil science at a university or community college.

The first part of the answer requires a discussion of soil formation. Soils form as the rocks in the region (called parent material) are broken down and "weathered" to form soil. This is a complex process involving physics, chemistry, and biology. Rocks are broken into smaller pieces by gravity, freezing and thawing, and the effects of water. Some of the minerals in the rocks are then further modified by the water which dissolves the readily soluble components and carries these minerals away. This "weathering" of rock is enhanced by biological activity.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms and the NMSU Horticulture Publications page.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at, or at the Desert Blooms Facebook.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!