Nursery producers create their own substrates by mixing two or more components. Components are often regional and based on available resources local to the nursery operation. Outdoor container nurseries use bark as the primary component mixed with one or more other materials to create an infinite number of possible substrates. Yeager and Newton (2001) reported that at a hands-on workshop in Hillsborough County, FL, nurseries brought 40 soilless substrates used for containerized nursery production for analysis during the workshop. Twenty-six of these substrates were unique and comprised of 16 different components. Similarly, Blythe and Merhaut (2007) documented the relationships of 127 different substrates, which consisted of 11 organic and inorganic components commonly used by nursery growers in California. The aforementioned papers illustrate the broad number of substrate components and virtually unlimited number of combinations that nursery growers use.
Jenkins and Jarrell (1989) attempted to validate Eq. . They found that linear relationships between measured and predicted properties of bark:sand and bark:perlite substrates were good for bulk density (Db) but mixed or poor for other parameters such as total porosity (TP), air space (AS), and container capacity (CC).
The most common substrate components use in the Oregon nursery industry is douglas fir [Pseudotsuga menziesii Mirb. (Franco)] bark (DFB), sphagnum peatmoss, and pumice. Each of these individual components has been studied. Buamscha et al. (2007) evaluated physical and chemical properties of fresh and aged DFB and reported that aged DFB had lower AS and higher CC compared with fresh DFB. These results were similar to findings reported by Bilderback et al. (2005) that aged pine bark increases CC and decreases AS compared with fresh pine bark. Puustjarvi and Robertson (1975) provide a thorough review of the properties of peatmoss. They state that one of the most important properties of peat is its capacity to absorb and internally retain large quantities of water. The amount of water held by a given weight of peat can be 15 to 20 times its own weight depending on peat type. Pumice is a porous igneous rock found primarily in volcanic regions of the world such as the Cascade Mountain Range in Oregon. The impact of pumice on crop growth and container physical properties has been studied throughout the world, because pumice from each volcanic region has unique properties (Gizas and Savvas, 2007; Gunnlaugsson and Adalsteinsson, 1995; Lenzi et al., 2001). Buamscha and Altland (2005) documented the physical properties of pumice used for containerized nursery production. Pumice is usually added to bark or peat substrates to hypothetically increase aeration, porosity, and drainage; however, there are no or little data to support this hypothesis.
As a result of widespread use of peat and pumice as an amendment for DFB in the Oregon nursery industry, the objective of our research was to document the effect of these components on the physical and hydrological properties of DFB substrates. A secondary goal was to determine if prediction algorithms such as those proposed by Jenkins and Jarrell (1989) can accurately predict physical properties of DFB, peat, and pumice mixes.
Blythe, E.K. & Merhaut, D.J. 2007 Grouping and comparison of container substrates based on physical properties using exploratory multivariance statistical methods HortScience 42 353 363
Breedlove, D., Ivy, L. & Bilderback, T. 1999 Comparing potting substrates for growing ‘Hershey Red’ azaleas Proc. Southern Nurs. Assoc. Res. Conf. 44 71 75
Buamscha, G.M., Altland, J.E., Sullivan, D.M., Horneck, D.A. & Cassidy, J. 2007 Chemical and physical properties of douglas fir bark relevant to the production of containers plants Hort-Science 42 1281 1286
Fonteno, W.C. 1996 Growing media: Types and physical/chemical properties 93 122 Reed D.W. Water, media, and nutrition for greenhouse crops Ball Publishing Batavia, IL
Fonteno, W.C. & Bilderback, T.E. 1993 Impact of hydrogel on physical properties of coarse-structured horticultural substrates J. Amer. Soc. Hort. Sci. 118 217 222
Gizas, G. & Savvas, D. 2007 Particle size and hydraulic properties of pumice affect growth and yield of greenhouse crops in soilless culture HortScience 42 1274 1280
Lea-Cox, J.D. & Smith, I.E. 1997 The interaction of air-filled porosity and irrigation regime on the growth of three woody perennial (citrus) species in pine bark substrates Proc. Southern Nurs. Assoc. Res. Conf. 42 169 174
Lenzi, A., Oggiano, N., Maletta, M., Bolaffi, A. & Tesi, R. 2001 Physical and chemical characteristics of substrates made of perlite, pumice and peat Italus Hortus 8 23 31
Lowder, A.W., Kraus, H.T., Warren, S.L. & Prehn, A. 2006 Nursery production of Helleborus sp.: Substrate irrigation Proc. Southern Nurs. Assoc. Res. Conf. 51 36 39
Milks, R.R., Fonteno, W.C. & Larson, R.A. 1989 Hydrology of horticultural substrates: II. Predicting physical properties of media in containers J. Amer. Soc. Hort. Sci. 114 53 56
Ownley, B.H., Benson, D.M. & Bilderback, T.E. 1990 Physical properties of container media and relation to severity of phytophtora root rot of Rhododendron J. Amer. Soc. Hort. Sci. 115 564 570
Pokorny, F.A., Gibson, P.G. & Dunavent, M.G. 1986 Prediction of bulk density of pine bark and/or sand potting media from laboratory analyses of individual components J. Amer. Soc. Hort. Sci. 111 8 11
Puustjarvi, V. & Robertson, R.A. 1975 Physical and chemical properties 23 38 Robinson D.W. & Lamb J.G.D. Peat in horticulture Academic Press London, UK
Tilt, K.M. & Bilderback, T.E. 1987 Physical properties of propagation media and their effects on rooting of three woody ornamentals HortScience 22 245 247
Yeager, T. & Newton, R. 2001 Physical properties of substrates evaluated during educational programs in Hillsborough County, Florida Proc. Southern Nurs. Assoc. Res. Conf. 46 74 77