Center for Transportation Research and Education

About the research

The Missouri gravel bed (MGB) concept originated from the practice of ‘healing in’ the roots of plants into moisture retaining material until the landscape site was prepared. While the initial MGB design was used just to extend the bare root tree planting season, this project proposes to test the ability of the gravel bed method to function as a year round production option for growers in Iowa. The objective is to grow trees with more fibrous root systems which are easier, more vigorous and economical to transplant and to improve the yearly above and below ground growth, making better quality trees marketable in less time. The aim is to test and demonstrate to growers the efficacy of this new tree production method as a way to reduce production costs while providing technical information to speed the adoption of the production method.

If funded, this project will inform multiple industries including nursery, municipalities, and natural resource agencies and we would anticipate that it would produce trees with a higher success rate of survival in the landscape. This study is designed to provide initial results within a 30 month time frame and will utilize resources (established irrigation mainlines, mowing, weed control and other infrastructure) at both the Iowa State University (ISU) Forestry Greenhouse and ISU Horticulture Research and Demonstration Farm. It will be incorporated into current ISU Extension and Outreach programming which will facilitate information exchange and adoption across a wide spectrum of the industry. Written material will be disseminated at local, regional and national nursery industry meetings as well as online at the Forestry Extension website.

Missouri gravel beds are not new, but the use and awareness of them has increased dramatically in the last 10 years. Researchers in Missouri and elsewhere have shown the efficacy of the systems but are unaware of research that evaluates the year-round seedling to transplant production scenario. A better understanding of the MGB system as a viable commercial production option and the ability of these systems to balance root structure, fine root production, and above ground growth to economically produce a merchantable tree from a bare root whip solely grown in a MGB is needed. For growers, retailers, municipalities, and homeowners the impact of such a production system is potentially substantial.

The MGB system could overcome several disadvantages found in the three most common production systems. It should allow for substantially more roots to be retained than the B&B method, create a plant with fine root mass that equals or exceeds container grown seedlings with virtually none of the architectural problems (e.g. girdling roots) that plague most container derived trees in 20-30 years. Additionally, it should eliminate dormant season harvesting and storage challenges (temperature, and humidity) until planting that limits the bare root production method.

Although upfront costs associated with the MGB production method might be higher, the entire system is reusable and if trees are produced faster, are of superior quality, are more economical to ship and plant because they are lighter and more compact, the return should be greater for the grower, municipalities, and landscapers. Trees produced from this system should also have higher transplant success rates reducing the 1 year plant guarantee replacement costs. Long-term, the impact will be realized with healthier trees that are able to withstand both disease and insect pressures on the landscape and harsh landscape settings while increasing benefits to air and water quality.