In the past 10 to 15 years a major marketing avenue for nursery crops—bare root tree field production—has declined. What was once a profitable mainstream production method for many nurseries has dwindled due to increasing demand for year-round planting and the greater flexibility of container production to meet that demand. Research underway through the AAES is looking at new production options for the bare root market that may rejuvenate the bare root market.

      Container-grown plants are shipped and sold in the containers (usually plastic pots) in which they are grown. Container production allows producers to grow plants in higher densities, using land that is not suited for field production. Since you do not have to prune container plant roots like you do with bare root trees harvested from the field, you expand the window of opportunity for sales, shipping and transplant survival of trees. Bare root tree planting is normally limited to the dormant plant season from about November to March, where as container plants can be planted year-round with high expectations of survival. However, container production also has its drawbacks. Producers must water and fertilize plants more frequently, give them more winter protection, and worry about plants becoming root-bound and sometimes being knocked over by wind. Containers also are costly and it can be more expensive to transport them because of the added weight of growing media and pots.

      Bare-root plants are usually grown in the field, harvested when they are dormant, and shipped or sold with no soil around their roots. They are also are typically less expensive to buy and ship and are easier for home gardeners to handle. The problem with this production method is that the plants are only shipped while they are dormant (usually late winter and early spring), which limits the time of year that they will be available to consumers. Bare-rooted plants also have been root-pruned in the process of digging, leaving some of the roots behing when plants are harvested.

      In today’s nursery industry, bare root plant production is primarily used for liner (transplant) production. With increasing global markets and demand for exporting nursery crops, higher fuel prices and shipping costs, and increased production costs and shortages of labor, bare root production still has a niche in the nursery business. Since field production of nursery tree liners requires cutting of roots to harvest trees, container production of bare root liners with roots intact may offer a better alternative for liners destined for container production or transplanting to the field. Bare root trees for the landscape would offer obvious weight and space reduction for shipping over equivalent sized container trees. Bare root trees are desirable and/or required for export to many countries. Furthermore, if bare root trees offer similar transplant success and growth in the landscape compared to equal sized container trees, this would suggest a new niche for nursery producers.

       An AAES study sought to compare bare root tree production in five-gallon containers using Profile™ (a commercial, nonorganic, kiln fired, calcined clay ceramic aggregate medium) with traditional container-grown trees using pinebark or pinebark:peat container mediums. The study also compared effects of pruned bare root liners to nonpruned liners potted in containers to simulate current practice of using pruned, bare root field dug liners (see table below). In addition, the study looked at the relative ease or difficulty of removing trees bare root from containers containing the Profile medium, and evaluated effects of storage, transport, and transplanting trees to a landscape site to compare the survivability and growth of traditional container trees with the bare root trees.

        On April 1, 1998, 72 18- to 36-inch, container-grown, bare root liners of Ulmus americana Liberty L. elms were planted in five-gallon RootMaker™ Grounder containers at the Ornamental Horticulture Station in Mobile. RootMaker containers were selected because they feature numerous small drainage holes that prevent fine particles of Profile from leaching out the bottom of the container. Prior to planting, half the trees were root pruned with approximately 50% of the roots removed to simulate bare root tree liners from the field. Roots were left intact on the other half of the elms.

        Plants were harvested and measured for height and caliper (the diameter of the trunk measured at 12 inches above the soil line) on February 26, 1999. Profile was easily removed from roots by gentle shaking. Used Profile media was collected in a central area for reuse in the next production cycle. Bare root trees were placed in plastic bags and stored in a cooler at 38^o F for eight weeks until planting at the North Alabama Horticulture Station (NAHS) in Cullman on May 3, 1999. Twelve container and 36 bare root trees were planted at a 15-foot spacing in a landscape setting to evaluate the survival and growth of the trees after transplanting. Height and caliper were taken on January 25, 2000.

       Elms grown in Profile medium in 1998 had greater height at 7.6 feet compared to 6.2 feet in the pinebark:peat medium, and Profile-grown trees also increased growth among the nonpruned liners (7.5 feet) compared to pruned liners (6.9 feet). There was no difference detected when contrasting pruned and nonpruned treatments within the Profile medium or between the nonpruned treatments of Profile and pinebark based media.

       There was no difference in caliper among the treatments. Profile medium had a high pH ranging around 7.5 and some chlorosis was noted on the elms grown in Profile medium. There was 100% viability following transplant at the NAHS of the 36 bare root plants and the 12 container plants after one year in the landscape. Caliper growth of transplanted trees was greater in the container/pinebark based medium (1.3 inches) at the end of the 1999 growing season than the bare root/Profile-grown trees (1 inch).

       There was no difference in height for the trees planted bare root or in containers. Trees were 8.8 feet and 8.7 feet tall, which represented an average (mean) increase over the growing season of 2.7 feet and 1.2 feet for container and bare root elm trees, respectively. Height of root-pruned container liners after one year in the landscape (8.4 feet) narrowed the height deficit between the nonpruned trees (9.1 feet) to a difference that was not statistcially significant.

       Although new Profile medium was used in the study, physical properties of some previously used Profile with the new medium were compared. No differences were found between them for each of the properties evaluated including airspace (12.4% and 15.0%, respectively), water holding capacity (40.5% and 39.6%), total porosity (53.0% and 54.6 %), and bulk density (0.53 and 0.51 grams per cubic centimeter) for new and used media, respectively. It is important to be able to reuse the material due to the cost.

       Results of this research offer evidence of a potential niche market for production of bare root trees in containers that can be successfully stored, exported, or transplanted to the landscape with similar growth results. Reduction in growth of root pruned elm liners in the pinebark based media suggests potential increased growth of container bare root liners over field-grown root pruned liners. Further research is needed with additional species to verify this conclusion. Container size, root pruning treatments, or time-in-production adjustments need to be investigated for several species, including aggressive rooting species to evaluate the ease of Profile or other media removal from the roots. Previous studies with river birch trees (Betula nigra) under similar conditions resulted in root bound tree roots that could not be separated from the Profile medium.

Tilt is Professor, Sibley is Associate Professor, and Woods is Associate Professor of Horticulture; Caylor is Superintendent of the North Alabama Horticulture Station in Cullman and Hesselein is Extension Specialist at the Ornamental Horticulture Station in Mobile.

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