Allen D. Owings, Regina Bracy and Edward W. Bush

Tree and plant bark and similar resources are widely used in the Louisiana nursery and landscape industries and across the southeastern United States. At one time bark was considered a waste product of the timber industry until land-grant university research in the 1970s developed its use as a potting medium.

From using bark as a growth medium in container-grown nursery crops, to mulching our signature live oak trees, to the use of bark and similar materials in landscape soil and as squarefoot- gardening media, this product is a valued and needed commodity for growers, landscape contractors, retail garden centers, arborists and home gardeners. In Louisiana, approximately 2 million cubic yards of bark-related products, in bulk and bagged forms, are used annually in the ornamental horticulture industry.

In late winter 2010, the U.S. Department of Agriculture proposed a Biomass Crops Assistance Program. This new program would provide financial support to producers or entities that deliver eligible biomass material to designated biomass conversion facilities for use as heat, power, biobased products or biofuels. This government subsidy program significantly reduced availability of wood-mill-based materials – such as bark, soils with bark additives and mulch material – all of which are widely used in the nursery and landscape industries.

Although this program may have positively affected the forest industry, it severely and negatively affected the horticulture industry. Temporary bark shortages left growers and landscapers pursing new and additional bark resources. Retailers that sell bark and landscape soil in bags and by the cubic yard to home gardeners also were affected. The bark supplies that were available carried significant price increases, and some supplies that were available had greatly reduced quality.

This action came at the worst time of year for the horticulture industry during spring when the majority of bark resources are bought, sold and used. This action, which has now stabilized and has been capped via congressional action for the short term, made horticulture industry businesses even more aware of the current and future issues facing bark, mulch and media supplies. Nursery use of bark materials is lower than in previous years due to the economic slowdown and downsizing in production. Louisiana and other states in the Southeast, however, are showing significant nursery production increases in 2011 with more planned for 2012, so the availability of quality bark and other wood materials must increase in the next six to 18 months. Landscapers and home gardeners also continue to use mulch, bark and similar materials in increasing quantities.

The LSU AgCenter and many other land-grant universities are involved in alternative nursery media research, mulch studies, recycling forestry waste products and other applied efforts to provide affordable, quality bark, mulch and landscape soil for the horticulture industry. In Louisiana and other states, municipal and home yard waste material is being converted for use in horticultural operations. Natural Resources Recovery in Baton Rouge is a good local example. Research being conducted at the LSU AgCenter is focusing on:

• Finding alternatives to the use of pine bark. Examples include whole-tree products, hardwood bark from oak and cottonwood, and combinations of these products. Many projects show these alternative media, when mixed in the correct proportions, fertilized properly and irrigated appropriately, can produce acceptable growth in container shrubs and trees.
• Developing fertilization practices to adjust chemical components in alternative media to produce desired pH ranges and nutrient availability for maximum plant growth. This includes the application of amendments such as sulfur, iron sulfate, copper sulfate, gypsum, Epsom salts and others to supply nutrients needed for optimum production. Many times, production costs can be decreased and applications of dolomitic lime for pH modification can be reduced or eliminated. 
• Modifying particle-size distribution – an important and often overlooked physical property of nursery media – in hardwood bark can produce ornamental plants that were believed for many years to not have the capacity to be grown well in hardwood media due to pH and physical property issues.

Depth-of-mulch studies are beginning to show ideal mulching depths for Southern live oaks and other shade trees. Many times 6 inches to 8 inches of hardwood mulch or similar materials are used in landscapes when research shows that a 4-inch mulch depth is best. This could result in a 50 percent reduction in mulch use in some urban forestry areas.

In these times of reduced availability of quality mulch materials, bark and related amendments for landscape soil and bark for container production, users need to plan in advance and possibly schedule some production practices, landscape installations and other horticultural activities for times when bark materials will be available. Many commercial growers face the prospect of getting bark deliveries from multiple suppliers when a single supplier would have handled demand in the past. The quality of materials also needs to be checked on a regular basis. This includes physical properties of the materials (such as particle size distribution and water-holding capacity) as well as pH, stage of decomposition, product stability, uniformity from load to load, fungal activity, salt concentration and more.

Allen D. Owings, Professor, and Regina Bracy, Professor and Resident Coordinator, Hammond Research Station, Hammond, La.; and Edward W. Bush, Associate Professor,School of Plant, Environmental & Soil Sciences, Baton Rouge, La.

(This article was published in the summer 2011 issue of Louisiana Agriculture magazine.)