Verde Valley Soils - September 21, 2011
Jeff Schalau, Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

There is little that we can do to change our soil over the long-term. For example, if you have a sandy loam, you will never convert it into a clay loam or vice versa. However, we can significantly improve our soil's ability to produce a crop in localized areas through adding amendments, deep ripping, rock removal, etc. Many plants are well suited to grow in our native soils. In the case of annuals and vegetables, we must manage soil with inputs of organic matter and nutrients. This week’s Backyard Gardener discusses soils found in the Verde Valley and how to make our gardening efforts more fruitful.

The Verde Valley’s best agricultural soils lay on the terraces above the floodplains along the Verde River and its tributaries. These soils are often deep, well-drained, clay loams and sandy loams. If they are not currently growing a crop, then someone almost certainly has farmed them at sometime between 600 AD and the present. These lands are also vulnerable to periodic flooding. These alluvial soils are usually alkaline (7.9 to 8.4 or higher). If these lands have been fallow, then mesquite trees may be present. Once cleared, these soils are excellent for irrigated pasture, crops, and orchards.

Moving up off the river and creek bottoms, we usually find low hills and benches. Some of these areas can be very stony. You may see some large rock outcrops. This tells you the soil is likely to be very shallow. In the Cornville, Lake Montezuma, and Rimrock areas, you will find limestone. In Sedona, you may find red sandstone. Around House Mountain, the rock may be dark basalt. Each of these different areas often has native soils that are well suited to rangeland habitat. With ample work, they can be improved for crop production. If rocks are abundant and soils are shallow, then consider raised beds or other intensive methods for vegetable or flowerbeds.

Mesa tops can have relatively flat expanses with moderately developed soils. For the most part, these soils have the same limitations as the low hills and benches. In some places you may find moderately developed soils formed from basalt. Many times these soils have high clay content which swells when moist and shrinks as it dries. These soils are recognizable by deep cracks during dry periods. Soil scientists describe these soils as "vertisols". These soils severely limit woody plant growth because roots are severed as shrinkage occurs and cracks open up. Grasses often predominate these areas.

Caliche is a common soil problem in the Verde Valley. Caliche is a cemented soil layer that is found between 6 and 12 inches deep. It forms when calcium carbonate is leached from the upper soil layers and becomes concentrated in the subsoil. Our limited rainfall carries the calcium carbonate to a limited depth. Over thousands of years, the concentration of this material cements soil particles, gravel, and rocks together in an impermeable layer we call caliche. When planting trees and shrubs, you should test the drainage of the hole before planting. If standing water persists longer than 24 hours, there is probably a caliche layer present. In some cases, the caliche can be fractured with a digging bar (or jackhammer) to improve drainage.

Soil texture affects irrigation frequency and oxygen availability to plant roots. Sandy soils have abundant oxygen but they are limited by their ability to hold moisture over long periods and require more frequent irrigation. Clay soils have the opposite problem: they can have limited oxygen with slower water infiltration but can go longer periods between irrigation.

Annual flower and vegetable crops are demanding on soil resources and success can be greatly increased through the addition of compost (not raw wood chips or uncomposted mulch). Compost benefits soil in many ways. It helps bind soil particles together to improve structure. It also adds essential plant nutrients in readily available forms, improves soil water holding capacity in sandy soils and aeration in clay soils. Biological activity is also enhanced. Yearly additions of compost are required due to our warm summers and alkaline soils, which cause the organic matter to break down quickly.

Follow the Backyard Gardener on Twitter – use the link on the BYG website. If you have other gardening questions, call the Master Gardener line in the Camp Verde office at 928-554-8999 Ext. 3 or e-mail us at and be sure to include your name, address and phone number. Find past Backyard Gardener columns or provide feedback at the Backyard Gardener web site:

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: November 21, 2011
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