Optimizing Soil Conditions for a Re-emerging Iowa Grape Industry

Name and Position/Title:
Paul Domoto, Extension fruit specialist, Horticulture Department

Fiscal Year Submitted:

Supports Plan of Work Number:
130 Horticulture: Commercial and Consumer 

Title of Success Story:
Optimizing Soil Conditions for a Re-emerging Iowa Grape Industry

Beginning in 2000, Iowa has experienced a re-emergence of a commercial grape industry that was virtually wiped out by the early, indiscriminate use of 2,4-D herbicide.  The industry has expanded from an estimated 29 acres on 25 farms to a projected 1,200 acres on 400 farms when plantings are established in 2009.  Much of this interest in growing grapes has been from owners of small acreages looking to better utilize their land.  However, many Iowa soils are not well suited for grapes because of poor internal drainage, a high soil pH, or a low available nutrient supply, particularly potassium and zinc.  Because grapes are a perennial crop with an initial investment in excess of $5,600 per acre, an improper site or nutrient deficiency can be jeopardize the success of the enterprise. 

Assist perspective grape growers identify suitable soils and optimize the nutrient status of those soils before and after planting grapes though educational meetings, soil testing and petiole analysis.

ISU Extension has undertaken an effort to educate and assist perspective grape growers in identifying suitable soils and optimize the nutrient status of those soils before planting grapes.  In February 2001, a statewide workshop was presented that emphasized site and soil requirements for grape vines, and practices to prepare suitable sites for vineyard establishment.  Those materials were posted on a newly developed viticulture home page (http://viticulture.hort.iastate.edu).   From 2001 to present an average of two area-based sessions were presented per year covering vineyard site and soil requirements, and vineyard nutrition. In 2004, ISU Agronomy Extension developed a Soil Interpretations “Vineyard Suitability” website http://extension.agron.iastate.edu/soils/interpretations.html.

Each of these activities emphasized the importance of soil testing to optimize the nutrient status before planting grapes.  Extension area field specialists made on-site visits to determine the suitability based on topography and internal drainage characteristics, and encouraged perspective growers to collect and submit soil samples to the ISU Soil and Plant Analysis Laboratory, and established growers were encouraged to conduct annual petiole analyses once the vines came into production by submitting sample to private laboratories.

Outcome Statement:   
It is estimated that this these programming effort reached 80% of Iowa grape growers with soil samples from 327 clients representing over 400 perspective vineyard sites submitted to the ISU Soil Testing Laboratory for analysis. The Extension fruit specialist interpreted the test results and sent recommendations to the clients.  This effort has allowed clients to optimize soil pH, phosphorous, potassium and zinc content before planting grapes. 

Clients have also been advised to consider alternative sites for grapes because of excessively high soil pH and organic matter content, and potentially poor internal soil drainage situations.  In conjunction with petiole analysis, this testing identified situations where excessive magnesium in the soil was inhibiting the uptake of potassium, and has led to the recommendation that soil magnesium also be tested before planting grapes.  Based upon the results of these tests, only about 5% of the sites represented by the soil samples did not require any amendments before grapes.  The optimal soil pH for American grapes (Vitis labrusca) is between 5.5 and 6.0; for French hybridgrapes (V. vinifera x Vitis species) it is between 6.0 and 6.5.  At higher a higher soil pH, the vines lack vigor and productivity.  Based upon the soil test results, about 50% of the sites required acidification to optimize the soil pH.  It was also found that a high percentage of the sites required amendments of phosphorous (57%), potassium (40%) and zinc (80%).  Because grape vines have a relative high requirement of potassium and zinc, optimizing the level of these nutrients before planting will improve vine development and productivity.  Under optimal conditions of vine growth and culture it requires three years to bring a vineyard into production.  With an establishment cost in excess of $5,600 per acre and cultural expenses in excess of $1,800 per acre for each additional year without production, grape growers participating in the program have improved their chances for developing a successful enterprise that recovers investment costs in a timely manner.  By not planting in unsuitable sites for grapes, clients could save as much as $11,000 per acre in cost to bring a vineyard into production.


130 Horticulture: Commercial and Consumer 

Last updated: August 8, 2010
Page maintained by Julie Honeick, jhoneick@iastate.edu