Greenhouse and Nursery Growing Substrates

The greenhouse and containerized nursery industries utilize artificial root substrates composed of organic and inorganic components such as sphagnum peat, composted barks, rice hulls, perlite and vermiculite. These components are used to formulate composite substrates that have appropriate physical (total pore space, air-filled pore space, water-holding capacity, bulk density, wettability and drying rates) and chemical properties (pH, electrical conductivity and mineral nutrient content). In addition to the basic components, amendments such as limestone, wetting agents and microbial inoculants may be added to the substrates to adjust the physical or chemical properties.

My research focuses primarily on substrates and substrate amendments used by the greenhouse and nursery crops industries. Because the growing container, the substrate and the mineral nutrition program are closely linked, my research group also conducts research related to production containers (such as biocontainers) and mineral nutrition of containerized crops. A few of my lab's major research projects are briefly discussed below. (Figure 1)

Figure 1
Figure 1. Evaluation of characteristics of containerized substrates

New substrate components

A major focus of my research program has been the development of new substrate components. Several factors drive the need for the development of new substrate components. One is a need on the part of the greenhouse and nursery industries for suitable, consistent, sustainable and low-cost substrate components. The other is the need to effectively utilize various types of agricultural by-products. Towards the development of alternative substrate components, my research group has worked with various companies on the development and evaluation of new substrate components such as Growstones, PBH and Nature’s Natural. (Figure 2 and Figure 3)

Figure 2
Figure 2. New Guinea impatiens grown in (L) perlite- and (R) PBH-containing substrates
Figure 3
Figure 3.Geranium grown in (L) perlite- and (R) Growstones-containing substrates

Substrate amendments

Various amendments such as ground limestone, nutrient starter charges, biological amendments and wetting agents are added to substrates to adjust their physical or chemical properties. I work with various companies to evaluate the efficacy of substrate amendments as well as to develop new uses for amendments. A current project is focused on using various types of wetting agents to not only improve wettability but to also inhibit algae growth on the surface of containerized substrates.


Describing physical properties of substrates

The substrates laboratory at the University of Arkansas is equipped with various pieces of equipment (i.e. porometers, pressure plates, sieves, capillary tubes, etc.) designed to measure various physical properties of containerized substrates. My research group works with numerous companies and assists them in developing and characterizing their substrates. We are also currently developing new protocol for characterizing and labeling substrates designed for containerized production. One of the unique facilities at the University of Arkansas is our subirrigation greenhouse facility. This greenhouse is outfitted with 12 “mini” ebb-and-flood benches that allow for testing and numerous different substrates or different types of solutions (fertilizers, wetting agents, etc.) used in the fertilization or subirrigation process. (Figures 4 and 5).

Figure 4
Figure 4. Among the equpiment available in the substrates lab are tempe cells and pressure plates
Figure 7
Figure 5. Examples of mini ebb-and-flood units available for research

Biocontainer characteristics and performance

As the desire for improved sustainable practices and reducing the amount of waste plastic produced has increased, my research (in conjunction with Longwood Gardens and Louisiana State University) has been focused on evaluating the characteristics (i.e. strength, water usage, etc.) and performance (i.e. plant growth) of various types of biodegradable containers. (Figure 6)

Figure 5
Figure 6. Testing characteristics and performance of various biocontainers

On-site substrate analysis using ceramic-tipped vacuum tubes.

On-site analysis can allow managers to observe and track changes in their crop nutrition, see trends and make changes before serious problems occur. Typical testing methods have involved using the traditional substrate solution extraction methods of the saturated media extract (SME), the 2:1 or the pour-thru. Each of these methods has certain difficulties and limitations. My research group has been working (in cooperation with the University of Padova) to develop a simple, low-cost and easy extraction procedure using ceramic-tipped tubes. The solutions extracted using the ceramic-tipped tubes are being compared against the traditional extraction methods and procedures for use are being developed. (Figure 7)

Figure 6
Figure 7. Using ceramic-tipped tubes for on-site substrate analysis

Current cooperators and supporters of our research program include

  • Division of Agriculture – University of Arkansas

  • Longwood Gardens

  • Louisiana State University

  • University of Padova – Italy

  • Sun Gro Horticulture

  • Riceland Foods

  • TyraTech (Nature’s Natural)

  • EarthStones (GrowStones)

  • Hanna Instruments

  • BioWorks

Dr. Michael Evans, Professor